If he needs to buy a car anyway, that's a good idea. Even a soccer-mom minivan with a little conversion work could be really comfy. One of those teardrop trailers would be fun, but they are $13,000 plus for a new one. I considered doing something like that with a trailerable sailboat-- use in on the water or like a camp trailer.
Take a look at some of the trailers here, then think about building a small trailer on one of those hardware-store utility trailer frames. They will hold upwards of 850 pounds, so you could build a little box with a bed, icebox, portapotty and some sort of safe heater. They have used small coal and charcoal stoves in sailboats for a long time-- they aren't cheap though. One used model to look at is the Cole Stove. I don't think they are made any longer. Search on "marine cabin heater" and see what you get: http://us.binnacle.com/product_info.php?cPath=7_266&products_id=2283 for example.