So to start with, I'd remove all the lower aluminum trim, the hatch and prolly the fender area trim and see what that affords you. You may be able to gently use a heat gun to see if the glass/board laminant will let go of the studs and plate. On our coach under the dinette they used fiberglass/styrofoam cut out's from the doors and window for the base. What I was thinking if you wanted to do a test is take one of those and apply a little heat to it ans see if it lets go. Otherwise I think you're going to have to cut some paneling on the inside and do the dirty deed from there. You may be able to get somd of that corner tape that matches the paneling to patch it back up.