On my 1976 23 original tank, it had two or four (cant remember now) 90 degree elbows brackets on the top port and starboard sides of the tank that screwed into the stringers plus the tank was covered on port and starboard with foam. There were no walls on the bow or stern of the gas tank deck so all water that was not trapped by the foam could drain. The problem is the foam over time becomes more like a sponge and soaks up any water holding it against the aluminum tank walls. My old tank had lots of pitting on both sides and the bottom of the tank where it sat directly on the plywood deck. My new tank had no foam and ribs on the tank deck to elevate it approx ¼ to 3/8 above the deck. Plus a few holes to permit air circulation. The tank compartment also has cut out on the stringers to permit air to penetrate the tank compartment which also helps.
FellowShip
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Just for the Grins
Official Antique Classic SeaCraft Owner