Vapor Barrier

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This may have been asked and discussed before.....
Has anyone here used an electrical dehumidifier?
Down here humidity generally increases at night. The portable AC units also remove a lot of humidity from the air.
I really appreciate the input from Off Grid 24/7 regarding water vapor. I just got a Ford Transit 250 and am starting the work. After reading his comments on air flow, I'm considering a 1 inch gap from the bottom of the walls to the floor and, another gap at the top before the ceiling that I can cover with an attractive breathable fabric. This would allow airflow between the interior wall and the van skin to help evacuate any condensation and dry out the space in between. Thus two questions:
1. Would this work or does this even make sense?
2. What would be the desired insulation material to use for acoustic and thermal insulation that would work well.
Environment could be high-temp/high-humidity (southern USA) to moderate to cold-temps and low-humidity (Rocky Mountains).
I'm a newbie and can't afford a mistake.
I'm not entirely clear what Off Grid meant, but I think he was saying that the interior side of the vehicle's metal needs to ventilate because moisture forms on it. I see that as an almost impossible task, and I haven't really seen that advice before after reading tons about vapor barriers in vans. Essentially it sounds like he wants us to make a levitating cave suspended inside the vehicle... how one would get air flowing around it I don't know. Plus none of us want to sleep on the vehicles' stock carpet, and apparently the moment we put anything on top of the vehicle's carpet we're ruining the evaporation Off Grid said they engineer it for.

Think about how many houses have metal exteriors... are they all specially engineered to have air flowing between the exterior metal wall and the interior? I don't think so. I'm not denying that the mold he's observed occurs, but I might question if it's being caused by improper ventilation inside the camper instead, or just people who took too many trips to the humid South.

I'd be happy to be corrected.
I think the need for a vapor barrier is greatly exaggerated and have never given it the slightest thought, and I've lived in a van in some truly extreme cold! Insulate your van with Polyiso and tape the seams with silver foil tape and you will be very happy with the results.

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