This is a pretty common issue, and not just with CR products. On my '04 Cruiser I had to 'improve' the fresh water tank. The factory uses flat metal straps (3) and a piece of plywood. The combo of too few straps and too thin plywood is just a problem waiting to happen. Anyway, it was too difficult to replace the plywood, so I replaced the flat straps with 1" square steel tubes, (but like 6 or 7 tubes) that were screwed into the cross-member supports. Never had another problem with the tank sagging.
I never travel with a full tank. Instead I leave home with just 10-15 gallons and then fill the tank at the campground.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK