For the walls and ceiling of the van, Eva and I decided to go with simple white-painted 1/4" plywood. We sourced formaldehyde free plywood from Gennett Lumber, a local lumber supply company in Asheville. Though the finished wall and ceiling installation looks simple, it took Eva and I the better part of a few weeks (while juggling other projects) to cut all the pieces to size and get them to fit in their places.
Due to the irregular shape of the van, every piece of wall and ceiling panel needed to be cut to a specific shape. One at a time, we would measure, cut, and then fasten the panels to the interior of the van. Each finished piece was screwed in place, and provided a new edge to fit the next panel.
The trickiest wall panel, by far, was the one for the window behind the kitchen unit. Eva and I initially intended to cut the hole for the window a fair bit larger than the window, and let the plywood rest on the natural metal framing that surrounded the space. David had another, better idea. David and Eva quickly put together a bendy-plywood frame that was just larger then the window frame, cut it to match the curve of the installed window, adhered it to the wall panel, and cut out the material in the middle with a router. The finished product was a very clean looking trim around the window.
The ceiling of the van is supported by a series of ribs, which provided a convenient space to install insulation, and obvious locations to secure the ceiling panels. We wanted a little more space for the insulation than the ribs naturally provided, so we added a series of furring strips made of 3/4 plywood to each side of each rib. The wood furring strips were also much easier to fasten the ceiling panels to than the metal ribs.
We wanted to insulate the wheel wells in addition to the walls and ceiling, so we made some covers for them out of 3/4" plywood. The insulation was then stapled to the inside of the covers, and the covers were screwed directly to the subfloor.
Below: Progress pictures for making the tricky panel to go behind the kitchen unit. Full credit goes to David for the idea, and much of the work!