Winter-ready ski-trip foamy design

[IrrationalExhuberous]

After seeing this ski trailer a couple months ago I've become obsessed with building my own ski trailer.
I then realized that copying that trailer would be: too expensive X4, too heavy X3, and not warm enough X2.

After rolling a couple designs around I've settled on building a foamie. I don't think I would begin construction until next summer and wanted to hash out some designs in the meantime

Key features:
- Enough insulation to stay warm when it's 0 degrees overnight.
- Light enough to be towed by a subaru outback (~2000 lb).
- Big/airy enough to allow climbing in wearing ski gear, not getting the bed wet, and clothes drying overnight.
- Wind shedding enough to not toss me off an icy, winding mountain road.
- overall be able to handle several days in snow.

I really wanted a standy, but at 6'5 in ski boots my first drafts were all too big for wind shedding. I went way smaller trying to hit the 4x8 trailer frame size but it was going to be too hard to keep everything dry.

I settled on something in the neighborhood of 6x12 footprint. crawl in / slouch height, about 50/50 bed and flooring.

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I think the walls will be either 3 inch XPS or two layers of 2 inch XPS glued together to make 4 inch walls. (I can't seem to find a source for the 3 inch foam in the state of oregon). Additional rigidity will be provided by OSB ribs running as arches up the sides and through the roof. Windows will not open, but be hand-built double pane acrylic windows following this construction style. with dry outside air instead being provided by dry vents cut into the walls with computer fans.


I went with a gable roof to shed wind and snow, which I'd never seen before. Maybe it won't shed as much crosswind as I think. I'm a little concerned about the roof seams leaking longterm ( but this should should not see prolonged rain, only snow). I was originally planning a PMF skin but concern for the roof seams is making me reconsider fiberglass.

There will be no plumbing at all, maybe a composting toilet or maybe nothing but a bag.

in terms of power, It seems like solar is out of the question most of the time and instead I should just rely on significant battery banks for my primary power. This would only be for charging phones and other gadgets, and powering a heater. I'm considering not even wiring lights and using a combination of lanterns and battery power stick on lights in key locations.
Cooking would probably just be a single burner camp stove (and maybe 12v electric kettle for a cup of cofee in the morning).

For heat I expect a sealed/vented propane or diesel heater (I wish there was a discount propex available like there seems to be for diesel).


Am I on the right track?

[linuxmanxxx]

Since your in no hurry you might want to think of a pop-up rectangle that sits the height of your tow vehicle. Raised would give you a standing profile and be light.

Build a small mockup and see how well just 2"does when cold with a heart source inside. You might not need it that thick with a smaller volume space. See if a small doghouse size would stay tolerable with say a light bulb as a heat source. Many complain of being too warm sleeping in them.
Steve

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[IrrationalExhuberous]

Would definitely love the height a popup would give me.
- I'm not sure how to seal the edgesbetween the upper and lower cabin.
- not sure how to build a jack/lift that could support 4 cubic yards of snow.
- if breaking the top and bottom into two parts would compromise the strength too much.

[linuxmanxxx]

If you go with fiberglass it's easy the strength it'll have. You could still keep the peaked roof for the snow control. If you keep it light and be creative raising and lowering shouldn't be too difficult to design as well as securing it. I've been designing one in my head quite a while. A outie lip on top the inner part that the upper part flushes to with an innie lip would be a perfect seal. Exact length poles to wedge under upper lip that rests on frame 2 in each corner locks it all in place.
Steve

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[Pmullen503]

Couple things: Slope that front triangle for a little better aerodynamics. You could cover the gable with something slippery to shed snow, either aluminum or maybe HDPE.

In terms of thickness, you don't need 4" of foam. The limiting factor is how much air exchange you'll need for ventilation so there's diminishing returns for insulation.

I winter camp in my unheated foamy (2" xps.) Just based on which sleeping bag I need for comfort, I'd say that in the foamy vs a tent, there's about a 20 degree difference. Not so much the temperature per say but you lose much less radiant heat. I've tried various schemes for heat but just use the right bag and tough it out for the five or ten minutes it takes for the bag to warm up.

Another aspect for comfort is humidity. I've tried an electric heater which easily warms it up but the air is very dry. But even adjusting the ventilation to have an acceptable level of condensation, the air in the foamy is still a lot less dry than a tent.

[tony.latham]

I agree with Pmullen. You still need to ventilate and that negates some insulation.

Save you dimes and buy a Propex propane heater. They are not cheap. If you can’t afford it now, design it in and install later. No matter how much insulation you have you still need something to heat it.

Tony

[OP827]

I had similar design requirements for my build. Foamie popup could be more work, but I do not know how much more since I only build this one foamie popup. Check it out for some inspiration and good luck with your build!

[dogcatcher]

Go to a toy store and buy a couple of action figures that are right at 6" high. This makes a good 6" to 1 foot scale for models making. Build a few models using foam board, you can pick that up at Hobby Lobby or like stores i various thicknesses.

The pop up is a good idea, you can use removable solid insulated core pieces when the "roof" is raised. Look at the A Liner travel traillers for ideas. My version of a build would use a fiberglass pickup bed tonneau as the roof, but canvas walls since insulation from the cold is not an issue in west Texas. For us 4 foot walls, with a 2 foot cloth pop up would be fine.

I have never done this but in my mind 2 sheets of 1" thick insulation sandwiching a sheet of half in plywood should give a very solid 4 foot high wall. With a < shaped front and > shaped back, and a flat top. Total length of the "box" about 12 feet, total height 4 foot.

[IrrationalExhuberous]

Couple things: Slope that front triangle for a little better aerodynamics.

I drew a couple designs like that, but it really cuts down on the interior volume while really increasing the number of roof seams and bizarre faceted edges I have to match up.
It may be necessary though, I defer to the community wisdom.

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I try to make up some of the lost height by increasing the peak roof height but then I started to worry more about crosswinds.
It's also hard to figure out the interior layout that still gives me a bench seat right inside the door to sit on to take my snowy boots off.

No matter how much insulation you have you still need something to heat it.

For sure, I'm only wavering between shelling out for the propex for the quieter operation and altitude resilience vs getting the 200$ webasto knockoff diesel heater.
My goal is to have a pleasant temp inside such that I can hang out in there in baselayers for 14 hours of darkness.

Another aspect for comfort is humidity.

In most winter camper situations I've read about, too much humidity from snow on gear, exhaled water vapour, etc, is more often the issue. I'm hoping the temperature difference and the heater will swing this in the other way.

In terms of thickness, you don't need 4" of foam. The limiting factor is how much air exchange you'll need for ventilation so there's diminishing returns for insulation.

How does a house manage to stay warm in winter without suffocating you?
Given how much surface area this thing will have (given how far from round it is) i'm skeptical that 2" of insulation at R10 is enough to maintain a 50 degree f temperature difference between the inside and outside, which is my stretch goal.

[IrrationalExhuberous]

The pop up is a good idea, you can use removable solid insulated core pieces when the "roof" is raised. Look at the A Liner travel traillers for ideas. My version of a build would use a fiberglass pickup bed tonneau as the roof, but canvas walls since insulation from the cold is not an issue in west Texas. For us 4 foot walls, with a 2 foot cloth pop up would be fine.

A popup would definitely have to hardsided. It would be nice if I could raise and lower it in a storm without catching tons of snow in the process, and i'm not sure how to do that without adding a fabric tent outside of the rigid foam panels i'd have to put in place. Seems like it may turn out too complicated and too prone to failure for the amount of energy I want to put into this. I'm sadly the opposite of retired.

I have never done this but in my mind 2 sheets of 1" thick insulation sandwiching a sheet of half in plywood should give a very solid 4 foot high wall.

Hard core, foam exterior gets the sandwhich construction formula backwards, all the strength of the foam lies in its resistance to compression. Surrounding plywood it would only flex around it in tension (and maybe even act as a lever multiplying strain on the plywood. Seems like a lot more weight for little gain.

[IrrationalExhuberous]

I had similar design requirements for my build. Foamie popup could be more work, but I do not know how much more since I only build this one foamie popup. Check it out for some inspiration and good luck with your build!

That's a beauty. Digging through the details now.

[Pmullen503]

I was thinking that just the triangle bit at the roof could be angled back, the side walls would not change. The main part of the body runs in the wind "shadow" of the tow vehicle so it's not necessary to streamline the front all the way down to the frame. Another case of diminishing returns.

A house is nothing like a teardrop in terms of the relative volume of air per person. Even a well built house leaks some air. Though modern tight homes use an air to air heat exchanger for ventilation. The problem with a tear especially is that the volume of air per person is so low. It's possible to build a tear so tight that you can use up the oxygen over night! Same thing with the amount of water vapor you exhale, or from melt water from snow, the low volume of air means you need to ventilate to get rid of the water.

You can compensate with a larger heater but you still have to ventilate.

[IrrationalExhuberous]

You can compensate with a larger heater but you still have to ventilate.

Of course, I was going to just cut two holes in either ends and slap dryer vent covers on them with a computer case fan in the midsection wired to a AA battery switch glued to the wall. I feel that should manage O2 just fine and CO so long as I'm not running a propane stove more than few minutes.
I'm hoping I can maintain comfortable residential temperatures with those open with fans off or on low, paired with a small RV heater, for at least 3 nights between refueling.


edit:
open question is where I place the intake vs the exhaust relative to the heater vent and return. probably place both the intake and return rather close together near where my gear corner is and have the heater vent point towards the bedside floor and the outside vent the furthest corner by the bed?

[tony.latham]

You can compensate with a larger heater but you still have to ventilate.

Of course, I was going to just cut two holes in either ends and slap dryer vent covers on them with a computer case fan in the midsection wired to a AA battery switch glued to the wall. I feel that should manage O2 just fine and CO so long as I'm not running a propane stove more than few minutes.
I'm hoping I can maintain comfortable residential temperatures with those open with fans off or on low, paired with a small RV heater, for at least 3 nights between refueling.


edit:
open question is where I place the intake vs the exhaust relative to the heater vent and return. probably place both the intake and return rather close together near where my gear corner is and have the heater vent point towards the bedside floor and the outside vent the furthest corner by the bed?

AA battery? You’ll need a 12 volt source to run either a propane or diesel heater. You can find those fans in 12 volt.

A better ventilation system would be cracked screen windows and a ceiling vent. No power needed.

We always have ours cracked when we’re inside.

[IrrationalExhuberous]

I was going to just cut two holes in either ends and slap dryer vent covers on them with a computer case fan in the midsection wired to a AA battery switch glued to the wall.

AA battery? You’ll need a 12 volt source to run either a propane or diesel heater. You can find those fans in 12 volt.

I was just referring to the computer case fan, which runs on 5v normally but isn't picky, this is just for external ventilation. My original post talks about not really wanted to bother fully wiring this trailer and just use battery mounted touch lights here and there, similar for the exterior vents.

I also talk in the original post about my plan to have a 12v system which would power a cell phone charger, the heater and maybe a 12v kettle (though that may turn out to be too power hungry and slow compared to a little camp stove).

A better ventilation system would be cracked screen windows and a ceiling vent. No power needed.

If the roof isn't totally covered with snow i'm having a bad time and don't want to be there. vents must be shielded and in the walls. Also mentioned, my windows are going to be hand-build, double-paned,triangular, and not open.

The use case for this trailer is quite narrow. it will be 0f to 30f degrees outside and used for skiing. If the weather is nice i'd rather be backpacking.