I have a 9.6 2500 series, I replaced the hdpe (puck board) with 5/8 painted marine plywood across the entire bottom of camper. Bigfoot chopped out huge areas of structure and then used 1/8 hdpe to cover the holes. This is one of the reasons why the overhang is sagging. The overhang and wings are being crushed or pushed upward by the weight of the camper above, they are just limp noodle without any bottom structure. The plywood gives the bottom structure again and it eliminated 90% of the sag in my camper. I also laminated 1/2 inche plywood along the basement walls. With the plywood in place I was also able to put some extra thickness of foam insulation between the plywood and the grey tank, this removed some of weight from the problematic seat belt straps.