So, screwing into the metal frame is what I did. I will see how that works before I worry about added complexity. I didn't work on the skin given it isn't a requirement to use the camper. Today I focused on the dresser I bought. I wanted it to fit directly onto the wall. In order for that to work I had to cut out part of the dresser at the bottom because the wall has a 3 3/4" bump in it for the bed rails.
In this pic you can see the bump for the top rail of the truck bed (middle of the screen) and the bump for the wheel wells in the truck bed. I am putting the dresser snug against the side of the wheel well bump (not the face). Doing it like this means I only have one bump to cut out of the dresser.
So I marked the cut and began cutting. I had to cut from the left side of the dresser and the back. The right side doesn't get impacted by the bed rail bump.
It fit perfectly. It is a five drawer dresser and the bottom two drawers will have to be modified. I will have to remove about 2" from the depth. They are 22" deep so it isn't much of an impact.
The dresser is actually bigger than I want so eventually I will build something custom that will use most of the wall on that side. In this pic you can see how the lower drawer sticks out. That is because I haven't cut the 2" of depth on the drawer yet.
Not as cool as a camper build but this will have to do.