Yes I fabricated everything from scratch, did all the electronics and even wrapped all the panels in two-tone leather. Next step is the cherry wood doors on all the cabinets to match the woodgrain dash.
I used 3/4" oak plywood ($40 a sheet) for the cabinets because I thought I would be staining all the cabinets, however I later decided to wrap it all in leather. For the bulkhead, depending on where you want to put it, get large enough pieces of cardboard and make some templates. The Sprinter has ribs all along the roof every 2ft. or so which you can use to support your cabinets. I also put a 1x2 cleat all along the side walls to support the bottom of the cabinets. I glued and screwed all the panels together and to the van itself.
This may not apply to what you want to do, but In order to have rounded corners for the cabinet edges, I ripped 3" PVC pipe along it's whole length, so I ended up with 4 quarter round 10' long pieces, then I attached them to the face and bottom of each cabinet panel to make the rounded corners. Sort of like the way you make bullnose corners in drywall. Then wrapped all panels in 3/4" thick upholstery foam then leather. Hope this helps.
John