That same day, walls went up. You can see how tightly the insulation fits within the frame. You can also see that I will have a challenge of attaching the outer skin of plywood. The reason I did not attach it to begin with is so that I could drive screws from the side walls into the front wall frame. This is the technique used throughout most of the trailer. If I were to pull out some of the rigid foam pieces, you could see that the walls are attached to the trailer floor through the bottom framing member. Plenty of caulk squished in between as well. The 1x4 scraps are temporary supports to keep the walls at the proper edge of the floor while I attach them. The exterior plywood will cover the side of the floor and extend all the way to the bottom edge of wood.