Insulation without Rust?

[Bicycle Bob]

I'm moving the mini-camper interior to its new home in the Chevy Sprint Coupe, and this time, I want it well insulated. However, I see the amateurs on YouTube having struggles with vapor barriers, and it certainly seems like a steel body would produce a lot of condensate if warm, moist air has access. It could also freeze, creating a whole new range of problems.
Does anyone here have experience with this? I'm currently thinking of having the steel completely covered with closed-cell spray foam, behind thick styrofoam, but wonder if moisture would still infiltrate. I'm also considering coating the steel with epoxy, and then using epoxy to bond the foam on, but not with a close fit everywhere.

[Piotrsko]

Most foams build a water resistant skin, some outgas various compounds during cure which can lead to corrosion (different than rust, but same effect). The msds published online tell what to expect and are available before you purchase.

I would use a waterproof primer of some sort both for waterproofness and adhesion

[Joggernot]

I know nothing. Have you considered the "Paint" used to seal the basements of houses? Seems like that might work, if it will adhere to the paint/steel of the vehicle.

[hayden55]

The issue is the breathing human inside such a small space brings the relative humidity to damn near 100%.

Below like 70 degrees all surfaces are at dewpoint. Windows, metal, etc... Gotta leave the windows cracked to get airflow or the inside just gets soaked.

My only thought is attach a hose to your mouth and evacuate your breathing through an exhaust vent to the outside lol.

Or maybe a dehumdifier/mini split in there. But small stuff is hard to find.

[Ecky]

Best bet is a dehumidifier.

[Bicycle Bob]

Thanks, everyone. As far as I know, a speck of rust will always grow under new paint unless it is sealed with epoxy. Everything else is micro-porous due to solvent evaporation or unreacted catalysts. It has certainly stopped my underbody rot. So, I'll probably use a coating of epoxy, but there's still potential for frost damaging the foam where it meets the metal, or building up where it does not. I could drill holes in the foam sheets and do the gap-filling from the middle, and then seal the outside of the foam, but one careless ding and humid air would still get in. So, now I'm thinking of using cotton rope to make drains. It would only admit air slowly, but it would quickly wick away any liquid whenever it thawed.