I am just going by what I saw at the factory in 1998. I just watched as they picked a wall unit up and proceeded to adjoin the two. I did a lot of work on it but I never had a broken frame so didn't have to do what you are doing. From what I saw it was exactly as I wrote earlier. There very well could be some ears/flanges like JSO said on the underside. My model sat on the floor and was screwed up from the bottom into the aluminum wall structure. It was not fixed to the frame. If it is moving that much I think the screws in the top have pulled out and probably a bolt or two on the main deck has pulled loose as this is a vacuume bonded wall and very rigid. You will have to take the fiberglass off from the pin area to the bay opening and access the screws from underneath
