A new thread in wreck dot about board storage got me Googleing for a rack design I'd found many years ago. Intended for surf boards, it is stupendously obvious and simple and brilliant. Ladies and Gentlemen, the Ply Rack:
Check out the Plyrack web page and see how the thing folds up if you need to get it out of the way. I think there is an idea here for van board racks too...swinging arms allow the van to carry oversized objects if needed.
With a single sheet of plywood (I'd get 3/4") 4 hinges, some screws and a jig saw you can put this thing together. Cool!