I started to camperize my Toyota Sienna 2008 AWD minivan by taking out the back seats and building two wooden boxes. The 6 bolts were easy to remove, and the seats taken out. The back most box is attached to the car using the same 6 bolts. The second box in the middle is attached to the back box by screws. The wood is 3/4 inch plywood and 2 x 4 wood. Total cost was less than $200. Each box has a lid, with the back one being removable. This allows storage of a large cooler, all the clothes and food for a weekend and other accessories. The front of the middle box is attached to a platform with a 10 inch high leg height. The mattress goes on top of all three.
We took the plastic from the seats to Home Depot to colour match the paint for the lids.We covered the sides with a vinyl decking material also purchased from Home Depot.