You can get really legit little campers that pull behind for as little as 10k. I have a 42' 5th wheel I live full time in, but just yesterday for fun we were getting some stuff fixed on ours and looked at the small ones. They had some with basically a shower, stove, sink, fridge, oven, table, bed, for like 10k. Even had small air conditioners. For 20k you can get way nicer ones.
I would get the van, or a truck with a camper shell (for storage of other belongings) and then get a small pull behind camper. It would be a million times more convenient to have your own fridge, bed, shower, etc. some have generators so they can run off gas and use water in your holding tanks, then can swing by an Rv site to dump the tanks in their sewage. Right now we pay 600/mo at our location which is steep, but my next place in moving to will be 400, as have some past places.
I know slightly less mustachian, but if you're selling your house and doing all that, might afford yourself a little comfort, plus, go look at a few and it'll be 1000x easier to convince the wife.