I'm installing a new v shaped tank in my boat. It sits in the middle of the boat but the angle of the tank is a bigger than the hull. It sits good on the edges but there is a about a 2" gap in the middle to the hull. Its a 56 gallon and is about 70" long is this normal or should I be concerned that all the weight is on the edges?

build a frame for it. start with a two by four or 2 one by fours or a 5/4 by four until you get thickness right straight down the keel to support the center. also need 1/4 inch or so black neoprene-i think- foam pad under tank. looks like wet suit material. only it is closed cell foam. doesn't soak up water. 56 gallons 6 feet long. i am guessing only about 3 feet wide. 2 more longitudinal "stringers" between center and edges you could probably get away with. ideally you want a marine plywood box set up off the keel so bilge water can't get to tank and tank is 100 percent supported by foam-padded wood. but 56 gallons is about 280 to 300 lbs of fuel. only about 60 lbs on each support point with less than a foot unsupported between each. i don't think that is enough area for flexing to cause metal fatigue. use cedar. stands up to water better than anything but teak or mahogany. tab the boards down to hull. i don't think glassing them in fully is necessary. make sure water drains past everything. if floor above tank is not a hatch which can be removed, make it so now.

Or you could just foam it in. Just use the right foam.

and run a piece of 1-1.5" PVC pipe under the center of the tank for water to drain through.

no foam. traps water and rots out the tank. just because OEM people do it that way doesn't make it a good idea. they do it because it is cheap and quick.