Step 20: Insulate the walls - Discuss the LIP
Time for more of the pink foam. I cut to fit solid pink foam, 3/4inch. Used Titebond II glue to attach to walls.
One of the features of this build is that you add the headliner from the outside, instead of trying to hold it above your head from the inside. The approach calls for a pronounced lip all the way around the cabin. It's essentially the tops of all the spars and insulation cut a pre-determined distance from teh edge of the ply.
What is this distance? Will it is the thickness of the headliner, plus the spars. Such that, when the headline r and spars are added, it will create a flat surface for the exterior skin.
I created a little jig from a razor blade, a piece of headliner (5MM plywood) and a piece of spar. I deliberately went too high with the spars and pink insulation. Then I went back and I used this jig to score a line where I needed to trim back. See the pics.
THERE IS ALSO a lip along the bottom of the side wall. The spars and insulation also stop a certain depth from the bottom of the wall. That depth is the depth of the 2x2 subfloor plus the 3/4 inch floor ply. This lip allows the wall to rest on both the trailer frame (where the outer ply touches) and on the floor (where the spars touch).