I have installed a Lot of things in all types of vehicals . Vans Have U channel frames for strength . Theres really nothing there behind those channels . The main wire-ing is under the chassis and your inside lights will be in the roof typically. I use self drilling self taping screws and I use urathene adhesive between the item being installed and the channels.<br /> Urathene adhesive Can install blocks of wood directly to the skin of the Van to attatch other things to very effectivly and very securly.<br />Just make sure the metal is clean ,no grease, rust or loose paint, and clean it with lacquer thinner and a scotch bright pad. <br /> Just make SURE your self drilling screws are not TOO long and go all the way through the van . <br /> Another approach is to lay out you plywood side panels with what extra support you need where you need it using 2 x 4's or 1 x 4's, behind the walls, that are Glued and screwed in place . Then install the entire panel and self drill / tap screw into the channels. Its a very good idea to locate all your mounting holes LAST so they hit the channel dead on AFTER the test fittings. Get it to fit right first, then locate the channel mounting holes. Drilling through the floor you need to be careful and look things over from underneath the van to make sure you dont hit anything. like gas tank, Frame, hydrolic lines Wire bundles and soforth , and have axcess to the hole for nuts and bolts if your not using self drilling / taping screws . I typically dont use self drillers in the floor, I use Nuts and bolts .