Thank you for your interest in the build. The 1x2 is welded to the main frame, it has two purposes: The first is to give the floor a place to be sandwiched in and the second purpose is to give the walls a starting point. As far as the tubing bender, I only used one radius die (1 1/4 in ). For me the key was to write every bend down as I bent the first set then duplicated the bends/measurements. You have to get creative when on a budget. The dividing wall will stay: Front 2/3 is the cabin and the last 1/3 is the galley only accessible from outside. And as for your final question, all the interior structure is attached to the skeleton via self tapping/drilling screws. This is the reason the frame took a bit of time to figure out, had to know the end picture (where everything attached to) before I could call the frame done. Well I hope I answered all your questions. Thanks again for reading.