Hey guys need some help. I pulled my fuel tank (under deck) and removed all the foam. The tank sits on a shelf. It was foamed in, something I dont want to do. The tank is very long and narrow and tapered. Roughly 19" wide aft tapering to 14" forward. 85" long and 7" high. My problem is the shelf/ floor is not level. The last foot on each end is level, but the roughly 4-6 in the middle is not. Its probably 5/8-3/4 off (sagging) I want to reglass anyway for extra strenght, but I dont know what to use or how to level the floor. It doesn't have to be pretty since its under the deck, but I would like it to be strong. Thanks in advance!