DIY Squaredrop Pod Build: Pop-Up Roof, Insulation, and Weatherproofing Advice

[TheHoboHouse]

New to the forum. I'm building a 4x8x4 DIY Squaredrop. Some unique/tricky features are that it will:

• be a "pod" design (able to be removed from the trailer base), and
• it will have an angled, insulated pop-up on the roof, on struts, to allow for standing up in part of the inside.

I plan to be able to use it in snowy winter weather (Colorado) as well as warm desert areas (Moab), so it will have 1.5" insulation, as well as a galley with stove and water, electrical, solar, simple outdoor shower, awning, stargazer, fold-down table, mounted TV/monitor, starlink. I plan to be able to use it as an "office with a view" for remote work. Planning to seal with marine epoxy and use Raptor Liner for the exterior, with some rock plate, and possibly fiberglass around edges. I am an engineer, so I've but a good bit of upfront design work into this.

I really enjoy seeing all of your designs and thoughts. Nice to be part of the forum!

 

[Tony Latham]

Planning to seal with marine epoxy and use Raptor Liner for the exterior

I don't think epoxy alone will keep it from checking. Perhaps I'm wrong. This guy put his Raptor over bare wood:

Wood sided trailer is having issues. Suggestions wanted

Adding a layer of glass isn't a big deal, and it will keep the wood from moving.

Good luck with your build!

Tony

 

[TheHoboHouse]

Thanks. I *think* the marine epoxy (its the penetrating kind) should prevent the ply from checking if I really let it soak in or use multiple coats. This camper will see some extremes in temperature and be in dry climates, so its worth getting it right. I've definitely debated doing fiberglass with the epoxy, and will give it some more thought. (I don't really like the look of PMF, so have mostly ruled it out.) But from what I've read, penetrating epoxy + Raptor should hold up reasonably well. Preventing water damage is probably my single biggest design concern.

 

[WYWander]

Squaredroppers unite!

I'm curious to see your pop-up roof design. Are you considering a straight pop-up or more of a clamshell? I'm considering a clamshell on my next build.

Have fun with it!

 

[TheHoboHouse]

Yeah I settled on more of a clamshell, hinged on one end, struts to assist the lift. I'm looking to have some more headroom when sitting on the couch (trifold mattress), and at least a small area to stand up. I still have some details to work out, but the idea I'm liking is to have fabric sides, possibly with mesh vents I could zip open to, much like a car-top popup tent.

In fact, after I started designing it, it occured to me that I could look into possibly just finding a way to use one of those hardshell triangular cartop tents as the clamshell roof... Maybe by cutting on opening in part of its floor. That could give both headroom and a bonus "bunk". But I'm probably going to just stick with a regular DIY hinged clamshell.

I could also have insulated panels (wedge shaped in the sides) to pop in there if needed in harsher weather. That may not be necessary though with good heating/air and solar, just more efficient.

I'll need to consider ceiling wiring (has to run through the hinged side), vent placement/angle change, and need to make absolutely sure the hinge is watertight and that it seals when retracted/latched.

 

[Pmullen503]

If you want this to last, use cloth with epoxy. Otherwise use something like a marine varnish that will be easier to repair when the plywood inevitably starts checking.

Other than sealing end grain or edges on plywood, I would never rely on resin alone to waterproof large flat areas of wood.

 

[Tony Latham]

Other than sealing end grain or edges on plywood, I would never rely on resin alone to waterproof large flat areas of wood.

It just isn't worth the risk.

Tony

 

[TheHoboHouse]

Thanks for the advice! Are you saying that the penetrating resin, fiberglass strips over (just) the end grain on edges (not full body), PLUS the full Raptor Liner coating may not be enough? In other words, the Raptor would mean it's not resin alone, so is that sufficient or are you recommending the Raptor be applied only over full fiberglass (+resin) underneath?

 

[KCStudly]

That's what they are saying. Epoxy or even bed liner doesn't have enough tensile strength to keep wood from expanding and contracting and eventually, cracking through the coating and allowing water in to rot the wood.

Fiberglass weave has the tensile strength needed, and when saturated with epoxy forms a very good substrate for additional sealer and UV protective layers. We have seen several other builders ignore or just be unaware of this advice, to detrimental effect... could've, should've, would've "crying in their soup". The whole purpose of this site is to share good ideas and good results, and to try and avoid bad ones.

 

[Pmullen503]

Yeah I settled on more of a clamshell, hinged on one end, struts to assist the lift. I'm looking to have some more headroom when sitting on the couch (trifold mattress), and at least a small area to stand up. I still have some details to work out, but the idea I'm liking is to have fabric sides, possibly with mesh vents I could zip open to, much like a car-top popup tent.

Is this what you have in mind? This is my latest RC airplane hauler. Fiberglassed plywood, electric struts to raise the lid. It doesn't leak. (In progress photo)

 

[Brumasterm01]

Prior to building my little trailer, I built canvas truck bed tent to fit over a king-size mattress. The center of the tent was 6' tall. At the time I thought i needed the headroom for standing and moving around. After using it for several years, I realized that I rarely stood up in it. In such a small space, there was really no need to. Instead the additional headroom presented other issues, namely heatloss and inability to set it up in high wind conditions.

I was constantly working to redesign my frame to hold up to higher wind conditions. 50 to 70 mph gusts are not uncommon in our local deserts. Finally after spending a sleepless weekend in the desert, I sold the tent and built my trailer.

I guess my point is 4x8 space is really small. Do you really need to stand up? It's not like you're walking from the kitchen to bathroom.

Also, I built my 4x8 trailer on 4x8 HF frame. After building and sleeping it, I regret not building a 5x8 trailer on a 5x8 northern tool frame. An extra foot in width is definitely usable living space.

Anyway my 2 cents. If you're like me, you probably already had your mind set on how you want to build it. Have fun.

 

[TheHoboHouse]

Is this what you have in mind? This is my latest RC airplane hauler. Fiberglassed plywood, electric struts to raise the lid. It doesn't leak. (In progress photo)
View attachment 2410844

Nice. Yeah, similar to that concept, though the sides would have a fabric wall, hinge would be on top (liftable part starting and ending where my roof slant ends in the front and back, about 18" from the ends, so about 5' long), and it would raise about 2 feet.

 

[TheHoboHouse]

That's what they are saying. Epoxy or even bed liner doesn't have enough tensile strength to keep wood from expanding and contracting and eventually, cracking through the coating and allowing water in to rot the wood.

Fiberglass weave has the tensile strength needed, and when saturated with epoxy forms a very good substrate for additional sealer and UV protective layers. We have seen several other builders ignore or just be unaware of this advice, to detrimental effect... could've, should've, would've "crying in their soup". The whole purpose of this site is to share good ideas and good results, and to try and avoid bad ones.

Thanks. Makes sense.

I guess I was thinking that since the walls were not just ply, but a sandwich of ext. ply (1/2") + 1.5" of spars/framing & insulation + int. ply (1/4"), that it would have enough tensile strength after the resin + liner.

But it sounds like I should heed the fiberglass advice to be sure.

 

[TheHoboHouse]

Prior to building my little trailer, I built canvas truck bed tent to fit over a king-size mattress. The center of the tent was 6' tall. At the time I thought i needed the headroom for standing and moving around. After using it for several years, I realized that I rarely stood up in it. In such a small space, there was really no need to. Instead the additional headroom presented other issues, namely heatloss and inability to set it up in high wind conditions.

I was constantly working to redesign my frame to hold up to higher wind conditions. 50 to 70 mph gusts are not uncommon in our local deserts. Finally after spending a sleepless weekend in the desert, I sold the tent and built my trailer.

I guess my point is 4x8 space is really small. Do you really need to stand up? It's not like you're walking from the kitchen to bathroom.

Also, I built my 4x8 trailer on 4x8 HF frame. After building and sleeping it, I regret not building a 5x8 trailer on a 5x8 northern tool frame. An extra foot in width is definitely usable living space.

Anyway my 2 cents. If you're like me, you probably already had your mind set on how you want to build it. Have fun.

View attachment 2410916

View attachment 2410917

View attachment 2410918

Thanks. Nice. Yeah I'm on a HF 4x8 as well. I've already started my build, so I'm committed at this point, but I did go back and forth about going with a 5x8 instead... I definitely can picture it being nice to have the extra foot of width, and it would make sleeping 2 easier. But settled on the 4ft to match the HF trailer, and keep my first build a bit easier.

I agree I probably won't stand much, but I do want to be able to sit on my couch (tri-fold mattress), with a fold down table/desk in front, and what I realized when measuring is that headroom would get super tight just sitting. It's possible, but my head would be practically touching to ceiling.

Since it's a 4x8, it will also make it feel a little more spacious with some wiggle room. (I had briefly considered some kind of side pop-out, but it complicated the build too much for the benefit.)

I figure I can always put it down in high winds if needed, but like having the option.

 

[TheHoboHouse]

That's what they are saying. Epoxy or even bed liner doesn't have enough tensile strength to keep wood from expanding and contracting and eventually, cracking through the coating and allowing water in to rot the wood.

Fiberglass weave has the tensile strength needed, and when saturated with epoxy forms a very good substrate for additional sealer and UV protective layers. We have seen several other builders ignore or just be unaware of this advice, to detrimental effect... could've, should've, would've "crying in their soup". The whole purpose of this site is to share good ideas and good results, and to try and avoid bad ones.

I appreciate the feedback. One question... due to this being a "camper pod" design that I will load/secure and unload from the trailer (not permanently attached), the bottom will have more stress and impact than most (jack lifting and sliding it on/off. My concern here is that fiberglass on the bottom would be prone to cracking, which is the main reason I originally leaned toward not fiberglassing the structure. A nice coat of bedliner over penetrating epoxy on the floor side seemed like it would slide nicely and may hold up better to that "pod loading" stress than having crack-prone fiberglass in the mix. Do you think, at least for the bottom, I should skip the fiberglass (or use something else) to reduce cracking?

(I used 3/4" ext. ply and framed/cross-braced the subfloor pretty solidly with tighter 2x2s + insulation, and used steel L-brackets at the corners to handle the stress structurally.)

 

[Pmullen503]

Using cloth will make it LESS likely to crack and easier to repair if it does. You can mix graphite powder with resin to make a more slippery surface for sliding on and off. Works well on boat bottoms.

 

[Tony Latham]

penetrating epoxy on the floor side seemed like it would slide nicely and may hold up better to that "pod loading" stress than having crack-prone fiberglass in the mix.

An epoxy/fiberglass matrix over plywood isn't prone to cracking. Quite the opposite. It's much stronger than thinned epoxy over wood.

Tony

 

[KCStudly]

I would do the glass skin, but then bond on a couple of sacrificial oak runners or skeggs using a marine bedding compound. Reduce the area in contact (less friction), create more ventilation to keep moisture from festering, and protect against point loads (such as the tipping point when dragging over rear edge of trailer). Also having a gap underneath could be beneficial for lifting, such as with a fork truck, strap, or broad billed lever (again, to spread point load).

 

[KCStudly]

Taper the ends of the runners like wedges, or skis...

 

[Happy Clamster]

Depending on where you are with your build/plans, you might be able to use a couple of ideas from my latest clamshell build, although it's a TD not an SD: "saddleboxes" to extend WOA from 48" to 62", and walls that go up with the pop-up. It also has slideout bunks-- doable, but yeah, a lot of work.