As promised... some issues that haven't been covered yet. Just keep in mind that most of these would be personal preference for the builder and there's probably several ways to skin any of these cats. There are just my thoughts.
WindowsFor my first build, I plan on simply creating wood frames that I'll epoxy in place on the inside of the panel, then cut out the opening in the skin with a router and flush cutting bit.
DoorsDoors could be done just like windows if using commercially built units. My doors will be custom panels (because I'm crazy) with 180° hinges and square windows. One door on each side.
Wall-to-frame attachmentMy plan is VHB tape between the bottom of the wall and top of the frame. I'll also use 1/4-20 bolts up through the frame into the bottom of the wall panels using special T-nuts made for fiberglass/composites. Each wall panel will have one bolt.
Interior SkinningI'm still on the fence with this. One option would be to skin the interior after the entire shell is assembled. Plenty of people do this on their traditionally made TD's and it works great, however it means working inside, on a vertical (or overhead) surface and could require mechanical fasteners to hold the skin on the wall (even if using epoxy). As of today, I'm leaning towards vacuum bagging the skins onto the walls (and roof) before assembling them on the trailer frame, i.e. skinning a hole wall laying on the floor. This means all of the wiring has to be installed, and windows, etc... have to be thought of and planned for before the skins are done. Doing it this way will create the ultimate sandwich panel and have a clean, smooth finish without mechanical fasteners.
For those that don't understand what I mean by vacuum bagging, I'll try to explain. An entire outside part of the wall would be assembled; the individual panels would be glued together, XPS would be glued into the cavities, wiring would be ran and window frames would be installed. Once that is done, it would be laid on a long sheet of plastic (at least twice the length of the wall). Then epoxy would be spread on the entire surface of the wall and the inside skin (luan, baltic birch, or whatever) would be laid on top. Then the plastic sheet would be pulled over the entire wall and a vacuum would pull all of the air out. The result is that atmospheric pressure becomes a very large clamp that acts equally across all surfaces of the part inside the "bag".
WiringMy trailer will have a V-nose section that will house all of the electronics, batteries, wiring terminals and so on. I will home-run wires to all lights, switches, outlets, etc... No daisy chaining because chances are it will be a lot of work to open the walls up to fix something like a loose connection later on. I will drill small holes in the wall panel frames, similar to studs in a house, and run the wires along the top and bottom of the walls. I will also notch the foam for the wires to sit in with a router. The notching in the foam will be on the interior side, not the outside, mostly to avoid the higher surface temperatures from the sun beating down on a black surface. It will be a little tricky getting the wires from the side walls into the V-nose, but I have that mapped out in my head. The rear storage area and ceiling should be pretty straight forward.
CeilingI didn't mention this earlier, so here are a couple of comments. This trailer will be black (because I'm crazy), so I'll probably double-up on the insulation to stave off mother sun a little bit. The roof will be sloped to each side (higher in the middle), but the ceiling will be flat. This may create enough space for a pseudo attic that I'm thinking about using as an air conditioner plenum to distribute cold air evenly throughout the cabin vs one air outlet blasting cold air onto the lucky or unlucky person sleeping in the bunk next to the air conditioner.
Sorry for the long post. Thanks for hanging on.
Steve