There were several different methods used to insulate and cover the walls depending on the location. My van only has windows in the slider and the rear doors. Each area is discussed below:
LOWER CAVITIES BELOW THE WINDOW INDENTS
The lower part of the walls has three deep cavities. Two around the rear wheel wells and one opposite the slider door. They are about 20" high and about 4 1/2" deep. Outside the Transit there are plastic rub rails at the bottom of body that are held in place by plastic fasteners. These fasteners leak water into the interior. So first these were sealed with Loctite PL-S40 polyurathane "window,door & siding" sealant. Covered each fastener. Then I painted two coats of latex paint that had hollow ceramic balls mixed into paint. The balls supply some insulation. Balls bought from www.hytechsales.com.
Installed 1/4-20NC prebulbed inserts in existing wall holes. Then I glued in two layers of 1" thick Aerocel closed cell foam with Aeroseal contact adhesive. Both supplied by www.aerflexusa.com. The closed cell foam is flexible so it can be folded to get it through the openings. If there was a seam in the first layer, had the second layer cover the seam. Next was a layer of Reflectix. Reflectix has very little insulation value if an air gap on at least one side is not provided. With this installation there is about a 2" air gap between the Reflectix and the 1/4" plywood wall cover. Used 3M 77 spray adhesive to glue Reflectix to the top layer of closed cell foam. The plywood cover has a 1/8" layer of closed cell foam glued to the back of the panel with 3M 77 spay adhesive. The panel is held in place by PVC plastic 1/4-20NC x 1" bolts. The plywood wall cover dimensions were obtained by making a cardboard pattern. Cut the cardboard pattern to cover the wall and tape it in place. The location of the inserts in the wall can be found by using a block of wood and a hammer to deform the cardboard to determine the hole location. Hitting the cardboard with the wood block where the inserts are located creates a round indent in the cardboard that is used to locate the bolt holes in the pattern. Then the cardboard pattern is bolted to the wall. Any changes that need to made are noted on the pattern with a black marker pen. The centerlines of the bolt holes are marked. Pattern then used to cut the 1/4" plywood. Plywood is painted the van color.
UPPER CAVITIES ABOVE THE WINDOW INDENTS
There are four cavities to insulate. Used same insulation method as lower cavities but without the need to seal the plastic rub rail fasteners.
TWO WINDOW INDENTS IN BACK
These indents can not have thick insulation. Needed to limit insulation so I could obtain a bed length of 73 1/2" across the back of the van. First I painted two coats of insulating paint on the inside of the exterior sheet metal. Ford put two 1/8" thick noise reduction pads on each side of the van on the exterior sheet metal in two of the openings. To get a flat surface I added 1/8" thick Rattletrap to the panels that did not have sound deadening installed by Ford. Then glued in 1 1/2" blocks of rigid polyisocyanurate insulation onto the panels between the steel stiffeners. Used 3M 90 spray adhesive. Left about a 1/2" gap between the insulation and the steel stampings around the perimeter of the blocks for later use of spray foam to lock the blocks in place. Also made the rigid insulation in two pieces for each panel with a 1" horizontal gap between the panels in the center. The opening is not flat so the 1" gap keeps the two blocks of rigid insulation against the van steel. The corners of the rigid insulation were cut off so a hole was formed to be filled later with Great Stuff spray insulation. Next I used Great Stuff "gaps and cracks" spray foam around the edges to lock the rigid panels in place. Trimmed the excess spray foam with a loose hack saw blade so spray insulation was flush with the metal stiffeners that are between the panels. Next I glued 1" rigid insulation on top of the metal stiffeners to make the wall surface level. Filled in around the edges and in the corners with Great Stuff. Used a loose hack saw blade to trim the spray insulation flush with the rigid insulation. Covered the insulation with indoor/outdoor carpet glued to insulation with 3M 90 adhesive. Note on the Great Stuff is to warm the can before use. Foams much better warm.
ONE WINDOW INDENT BEHIND THE DRIVER'S SEAT ON LEFT SIDE
Same procedure as the two back window indents except eliminated the indoor/outdoor carpet. In place of the carpet I glued an additional 1 1/2" of rigid insulation on top of the 1" and 1 1/2" rigid insulation. Again put it up in sections and used the Great Stuff spray foam to fill the gaps and hold it in place. Trimmed off the excess foam insulation to get a flat surface. Covered the insulation with Reflectix. This wall is hidden behind the refrigerator/shower cabinet so paneling was not necessary.
There is about a 1 1/2" air space between the Reflectix and the back shower wall. Do not have any wiring buried in the walls. All cords are outside the wall and in or behind the cabinets. Did need to have cords pass behind the shower back wall. They just lay at the bottom of the air gap in the window indent supported by a 1'" closed cell foam pad.