If I knew how to weld my van would have come out much different. But my "found art" skills are still better than my woodworking.
I solved the "bouncy bouncy" problem in two main ways. My bench supports are aluminum locker room bench cantilevers from Rakks. (You can imagine the forces they're designed to withstand.) The bench/sofa/bed platform is made from Reese 15"x 75" atv ramps. Each ramp is 12.5 lbs but rated for 650 lbs. My three-ramp bed can thus withstand almost a ton of fun. Our bed size is 30x80 as a twin and 45 x 80 as a narrow double. (We like each other.) I could have a 4-section 60x80 but more typically stagger two 30x80's when I have a guest in lieu of my DW.
Everything KDs easily, a dropdown set of legs make for a two-section folding sofa, a couple of aluminum u-channels slip in to span the cantilever gap for the three section bed. The design got rebuilt twice to let everything fold flat to the walls and to let the bed assemble tool-free.
My primary design thought was to allow me to carry canoes inside on daytrips but the aisle space also often holds bikes. And I think my van should be able to work for a living occasionally---the clear floor span is great for plywood and I folded the benches to carry three stories of scaffolding for some stick house work.
My fold-away interiorDan