[gearhead]

Be thinking about what insulation you are going to stuff in the voids. Fiberglass will hold water, especially if paper faced. Maybe some foam shipping "popcorn" pellets?
My chloroplast was sagging and I worried about it coming loose. I got some light gauge angle "iron" that has slots and holes in it, like uni-strut does. I screwed that to the frame, side to side. Helped a lot. Used stainless steel self drilling self tapping screws from Fastenal. Not sure how far below the frame your new insulation is. Might have to use longer screws.