New member, new trailer design!

[reaver]

A little about myself.

A few years ago, I decided to build myself an off road trailer (this was in the middle of covid). My family and I are very much into going off grid, and getting far away from the crowds. We got tired of packing my 2003 Xterra with everything we needed for a 5 day camping trip, and after much deliberation, I decided a trailer was the solution to our problem.

Enter Groot 1.0:






But, as my daughter grows, and my wife and I get older (though, we'll be able to set up a tent for at least the next 20 years), I decided it was time to move to a square drop as a main camping trailer.

So, the design process begins. I know it's going to be a 5x8 main box, With an external kitchen box.



The exterior of the trailer will be skinned with 4mm ACM Panels.

This is sort of what I'm thinking for attaching the walls together, and supporting 1in rigid foam insulation:

Assembly:


Exploded View:


The interior cabin will be roughly 6.25 feet long, with the back storage area filling out the remainder of the main box interior space.

I'm also planning on putting a 2 foot x 3foot tall "fridge" box on the front of the trailer, with access doors on both sides. This will house my fridge, batteries, fuse blue, etc.

What I'm mostly wondering though, is whether this is a good way to attach the walls together, or is there another configuration that is better/more secure? All panels and walls will be both glued and screwed.

Thanks!!

[tony.latham]

So, the design process begins. I know it's going to be a 5x8 main box, With an external kitchen box.

Will the fenders preclude that? It's important for the axle to be at about the 60/40 point on the chassis frame.

Also... one reason teardrops work is because the entry doors are where a person's hips are. It makes for easy entry/egress. And note I used the plural of doors.

Tony

[reaver]

So, the design process begins. I know it's going to be a 5x8 main box, With an external kitchen box.

Will the fenders preclude that? It's important for the axle to be at about the 60/40 point on the chassis frame.

Also... one reason teardrops work is because the entry doors are where a person's hips are. It makes for easy entry/egress. And note I used the plural of doors.

Tony

Absolutely planning two doors. Not entirely sure on placement yet, as I don't have the frame. I'm hoping to pick that up this weekend. I should be able to move the axle farther back, if necessary. I won't know for sure until I measure the frame. I will say, towing wise, my current trailer has been remarkably stable, but I did my best to keep most of the weight forward of the axle (10-20 gallons of water, depending on needs). I need to measure the wife and I, and see how long it is from our hip center to the top of our head. That should give me a good idea for door placement.

I should also mention, while I have a welder, I don't have the knowledge or skill to confidently weld a trailer frame. I found this frame at Tractor Supply that will fit what I want to do perfectly:



I like this one over other options, as it uses tubular steel vs c channel or angle. The tubes are also about 1/8in thick. Should be MORE than strong enough, while weighing only 500lbs for the frame.

Thoughts on how I'm planning on assembling the walls?

[Pmullen503]

Before you decide on wall thickness you should probably source your doors and windows (unless you plan to build your own) to see what wall thickness they can accommodate.

What material is that for the interior walls? It looks about 1/2" thick which is overkill for plywood.

The flip out table is interesting. If you plan drawers, obviously the contents will move to one side when closed, which is not ideal. If no drawers, consider a collapsible sink to keep the side bump out as narrow as possible.

[tony.latham]

Thoughts on how I'm planning on assembling the walls?

Other than the foam, you didn't say what the other pieces were or what the structural members were.

Here's how I do my walls:



And the internal skeleton looks like this:



And of course, the voids are filled with 3/4" foam board.

I've used stick framing, and it is much more labor-intensive than using 3/4" CDX plywood.



Tony

[reaver]

Thoughts on how I'm planning on assembling the walls?

Other than the foam, you didn't say what the other pieces were or what the structural members were.

Here's how I do my walls:



And the internal skeleton looks like this:



And of course, the voids are filled with 3/4" foam board.

I've used stick framing, and it is much more labor-intensive than using 3/4" CDX plywood.



Tony

Good points. The main reason I plan on using stick framing is doe to the fact I want to be able to use 1 inch insulation instead of 3/4 in. I like to camp in the winter, and it gets hot here in Idaho during the summer. The extra insulation will double my r value {r3 for 3/4in, vs R6 for 1 in).

I the above assembly image, the wall structure is as follows.

Outer layer is 4mm ACM panel
1/5 in plywood
1x4 spars on the outer edge of the wall for strength with 1x2 inner supports (voids filled with 1 inch rigid foam
Inner layer of a really nice 1/4in ply

Does that make sense? I'm happy to sketch out a more clear drawing. I'm a 3d artist by trade, so it's easiest for me to visualize how it goes together if I build a 3d model like that.

I'm curious if I'm over thinking the joking between the floor and the wall.

[tony.latham]

I want to be able to use 1 inch insulation instead of 3/4 in. I like to camp in the winter, and it gets hot here in Idaho during the summer. The extra insulation will double my r value {r3 for 3/4in, vs R6 for 1 in).

You'll never convince me that a human can tell the difference a quarter inch of foam board adds. Especially in the summer since the windows and ceiling vent will be open as far as they go. Build it that way if you want, of course. It's probably more of an issue of finding 1" thick lumber.

But take a hard look at what windows and doors you'll be installing. They are built for specific thicknesses. (I get mine from Vintage Technologies.)

To me, wall insulation is more about preventing condensation on cold nights. I bought my first teardrop in 2004, and it had no insulation in the walls. On cold mornings, the water ran like the Snake River.

I too, live in Idaho. Salmon. What you'll find about a teardrop and heat is that you and your spouse will be the main problem, and that's taken care of with great ventilation--two screened windows and a ceiling vent fan. For the cold weather camping, save your nickels and install a Propex (propane) heater. Design the room for it at this build stage and add it later.



I install 2" of foam board in the ceiling (which includes the front wall) and the hatch. The 2" thickness is really about strength with 2" spars.





Tony

[Pmullen503]

One thing to remember is teardrops require a lot of ventilation because of the small volume inside. That means that you get into diminishing returns very quickly when adding insulation.

I've done some sub zero camping in my unheated foamy (2" XPS). Based on what sleeping bag/liner I need to be comfortable, I'd say the effect is like adding 15 degrees F compared to tent camping. The air is definitely not 15 degrees warmer, I think it's due primarily to less radiant heat loss from me.

[Simple_Abound]

I've camped in 20 degree to 90 degree weather with my homemade pop up square drop. If you don't have proper ventilation in cold weather you'll have condensation issues. With that I don't see a benefit to 1" insulation from 3/4". If it's in the budget and if there's a local reputable trailer builder I would recommend it, you won't regret it.There is great information on this site. Good luck with your build.

[working on it]

I've camped in 20 degree to 90 degree weather with my homemade pop up square drop. If you don't have proper ventilation in cold weather you'll have condensation issues. ...

I, too, have camped in both cold and hot weather in my homemade squareback trailer, but it was a range from 35F-105F temperatures. being in N.Texas/S.Oklahoma in the spring, early summer. The use and amount of insulation used really depends on when and where you'll be camping. I knew I'd be camping 99% of the time in warm-hot weather (even our winters are warm compared to other climes), so I really didn't consider insulating the trailer, until after I experienced cold sidewalls inside, when I'd roll over in my sleep at night (the inside width is only 46.5"). My solution was to put indoor/outddor carpeting squares on the sidewalls in question...problem solved.

There's been no condensation inside my cabin (except for the night when I had 1-2" of standing water inside, due to leaving a door cracked open during T-storms), because I have as much airflow as I'd ever need to push moisture out thru two side vents, two windows, or the humidity expelled thru the A/C. The waterproof side vents are always cracked open, 24-7-365, and usually have a computer case fan pushing or pulling air thru them. If more airflow is needed, there's an 11" fan that I can use, and the A/C fan can be added to that. Never any inside condensation, but on a warm/hot day or night, there's plenty of condensation on the exterior, when I run the A/C.

crude representation of airflow inside the cabin; there's always air moving inside and zero condensation

airflow and condensation reduction in my 4x8.jpg (304.36 KiB) Viewed 2326 times

...I've done some sub zero camping in my unheated foamy (2" XPS). Based on what sleeping bag/liner I need to be comfortable, I'd say the effect is like adding 15 degrees F compared to tent camping. The air is definitely not 15 degrees warmer, I think it's due primarily to less radiant heat loss from me.

My trailer doesn't have the inherent insulating properties that a foamy constructed from 2" XPS would have; 3/4" plywood walls (ceiling & floor, also) give little insulation, though my floor covering ( a rubber+carpet industrial mat) does provide a little. I have used between 4"-8" of foam mattresses, comforters and blankets in the past, to keep warm, but I've simplified my method in later years. I now use a 4" (folding) mattress, plus either a Coleman 20 degree or 50 degree sleeping bag, and one or two Lasko "My Heat" 200 watt "personal" heaters (located on an overhead shelf, since they don't have tip-over protection) I've used them for many years, when I've been stranded at work during ice storms and slept in the back of a truck with an aluminum shell in back, or inside my HHR Panel ...bought with such a use in mind...at temperatures down to 4F, using the 20 degree bag, plus blankets. I was a little cold in the aluminum shell, a little warmer in the HHR, but it wasn't too cold to sleep. Perhaps I should've taken my trailer to work? (a 120-mile round-trip) I'm sure it would've been more comfortable.

I've used two Lasko's for many years, even to heat under-sink areas (in my house, none in trailer) during sub-freezing weather

Lasko.JPG (113.29 KiB) Viewed 2326 times

[Tom&Shelly]

We have 3/4 inch foam in the walls and 1 1/2 in the ceiling and that's fine. The metal frame on our commercial doors is giving us condensation problems in cooler weather.

We couldn't find 3/4 inch foam so we built a large bow hot wire cutter and shaved 1 inch down.

Tom

[reaver]

Thanks everyone for the tips! I've decided to switch to framing the walls with 1x2 instead, to accomodate 3/4in foam. I do plan on running a diesel heater in the trailer. I'm looking at a 2kw heater (I don't have the money for a propex heater).

I've done some more sketching regarding door placement, and layout of the studs.



red lines in the side drawing are where my 1x2 supports will live inside the wall. Blue areas are filled with insulation.

Lower drawing has lines indicating what's what. I'm not entire sure how i want to frame out the roof spars yet.

If you look at the above image, I've included some basic dimensions. I measured my wife laying on the bed, and sitting up. The door is just about in the perfect spot. Moving it farther back makes it look odd, so this is where it's going to go. This is with a 26x32 rounded doors. These doors have screened windows in them. I'm undecided if I want one to have a full screen door, and one to just have a window or not.

I'm planning on going with a 14" Max Air fan.

In the above image, is it better to set the wall on top of the floor platform, and screw down, or would it be better to leave a lip on the bottom most layer of the floor, set the walls on top of that, then screw into the side of the 1x2 in the floor? In either scenario, the side walls will extend down around the outside of the floor, preventing any water from sitting on the floor plywood (though the entire trailer will be coated in epoxy. I'm unsure if I should coat layers before assembly though, and then again to protect seams, or just coat the box once it's assembled. I've also got somebody who's built many trailers (though mostly out of foam) to fiberglass the entire box, prior to laying my ACM panels down. Also, I'm researching alternatives to ACM. I LOVE the way it looks, but if I can do it cheaper, I'm certainly open to suggestions. I'm not sure I want to consider bedlining. I want a smooth finish for applying stickers and decals (yeah, I know, typical).

[tony.latham]

This is how my walls mate with the floor.



Screws also come in from the exterior horizontally.

Here's a video of me setting a wall. Note that it's also glued with PL3 adhesive.

https://youtu.be/bhF2dhvj4YY?si=N7L7V0ZvNrNOulaD

And note the ledge on the wall. It enables you to build the ceiling from the inside out.



Tony

[reaver]

This is how my walls mate with the floor.



Screws also come in from the exterior horizontally.

Here's a video of me setting a wall. Note that it's also glued with PL3 adhesive.

https://youtu.be/bhF2dhvj4YY?si=N7L7V0ZvNrNOulaD

And note the ledge on the wall. It enables you to build the ceiling from the inside out.



Tony

Awesome. Sounds like I have a solid plan for assembly. Of course everything will be glued as well.

I've not ruled out bedliner either.

I'll have to look into pl3. I have lots of experience with titebond 3. Which I still have lots of, but if pl3 is what I should use, then that's what I'll get.

[tony.latham]

I've not ruled out bedliner either.

I'll have to look into pl3. I have lots of experience with titebond 3. Which I still have lots of, but if pl3 is what I should use, then that's what I'll get.

If you go the bed liner route, make sure to fiberglass/epoxy it first, or there's a great possibility the plywood will crack. I used Monsterliner over fiberglass/epoxy on my last build.



I use PL3 when I need gap-filling properties that TB3 or 2 doesn't have and when I need more open time. TB3 has a ten-minute working time. That's not enough for a lot of joining on a camper.

Tony