Doing this for a van, you have the advantage of making the front of the space into a separate drawer that sides out the side doors. That way you don't have to have 8' of open space behind the van to open the drawer out the back.
Smaller more versatile drawers that way. You can even make two drawers that slide out of the side. One behind each door. That way one of the drawers can open with only one of the side doors open.
Another note: If the drawer design doesn't allow 4x8 sheets to slide in flat, below the drawers, you may want a slot to the left of the rear drawers, on the driver's side, where sheet goods can slide in vertically. Hope that makes sense.