I agree with Nature Lover..
That said I did it.. I did it when I was in the Miami area in Florida, Before summer Hit. the things I did I knew where not going to be completely permanent..
I have an 06 grand caravan.. and the first thing I did, was a bed platform with Storage under it. made it with 1x2 frame. plywood top, about 26"wide.. got a 2" memory foam mattress from wally world(full) fold that in half length ways. and that was my mattress.
Now I am in a place where I am able to build out my van properly..