PMF shower stall/bathroom

[ai4kk]

asking my question on here because y'all are the foambuilt experts
I'm hopefully getting ready to head out to Washington for a 3-month travelnursing assignment. While I have 2 acres out there with a small off-grid campsite on it, the assignment is about 150 mi away in Forks and I would be sleeping in my 4x4 Astro van between shifts and going back to my property on my days off.
Do you think PMF would work well and be cost-effective to build a shower / bathroom stall either at the property right outside of my truck camper or maybe even on the cargo rack of my van? The idea would be to have an insulated box that I can set my Mr Buddy in and use a portable hot water heater to take a hot shower before going to work. On the van it would probably be a very small wet bath narrow enough to fit between the taillights of the van but at the property I was thinking about a 4x8 bath house with enough room for a shower and separate toilet / changing area big enough to change clothes.
Whether I go with one idea or both, some of my questions are the same ... How do you get PMF to dry in a cold and humid marine environment like the Pacific Northwest in the wintertime? Is there a problem with frequent exposure to moisture like inside a shower? For the stationary shed, is it necessary to frame it or will it be strong enough by itself since it won't be mobile, at most portable if I move it from one part of the property to the other? Do I need to PMF the inside or maybe just a couple of heavy cuts of waterproof paint?
Any help for information would be appreciated

[linuxmanxxx]

Lowe's has a non reinforced plastic that would be far better for the walls. It's light and durable and won't hold mold or mildew in such a wet environment. I'd do both inside and out with it and could be made permanent or able to disassemble. Just use some polyurethane foam safe glue to adhere to the foam.
Steve

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[dogcatcher]

I have seen a deer blind made using PMF. It was a pentagon, about 5 foot across on the inside. Used 5 panels for the 5 walls, that were taped in place then covered with PMF. Roof was 1/2" PVC pipe that was bowed across the top. His roof cover was plain canvas that was stretched over the bowed PVC. The roof canvas was then painted with several coats of paint. The base was built with plywood over 2x4s.

I believe if you cover the interior walls with the plastic sheets that were already mentioned you would be in business.

The blind sits on a 5 foot high tower, and has survived 3 or 4 years of Texas weather and wind.

[linuxmanxxx]

Also if you take a 4x8 sheet on each end and angle down a half foot from front to rear 8'in front and 7 1/2' in rear, water runs off the back and a lot easier to not sag on top. If you can get 3/4" foam 1x? match the width and double on roof 1x2 standing on edge matches it or 1 1/2 if you can get it and it would be extremely sturdy. Pallets with a covering for floor let water run out underneath.
Steve

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[ai4kk]

This is why I asked here, y'all gave me some good stuff to think about. Already planning the porous floor...perforated rubber on palettes for the stationary version, steel mesh for the mobile one. Trying to find the plastic sheeting on Lowe's, closest I found was $34 for a 4x8 sheet. Will do more research and look other places as well, but that sounds like the same material. Might even look at one-piece shower surrounds, esp if I can find one used at a home surplus kind of place.
I'm liking the idea...not only for being able to take an off-grid hot shower in a heated room (last year I did a similar assignment in Raymond, WA and my landlord didn't have heat or hot water in his house until I bought a space heater then fixed the wood stove, and my son came to visit and fixed the hot water in the shower) so i know how miserable daily lukewarm showers in a cold room can be. I also like the idea of adding extra room that is tall enough to have a place to stand in without getting a bigger vehicle as I like my little 4X4 Astro van and love the idea of keeping the humidity and any stinkiness out of the van itself.
The fact that i can remove it and use the outside shower in the summer is a bonus
https://photos.app.goo.gl/jg4E6texnurqq2DP7