Thanks for the tip on the hose clamps.
The T&P currently goes overboard. Isn't that better than in the bilge?
Air space under the tank. Are you saying I should shim up the tank a bit? OR is there space between the outer housing and the tank in which insulation is sandwiched? The insulation is a bit wet at the moment since the 'whale' fittings are leaking.
I agree, overboard is better.
Yes, shim up the tank by putting 1/2" (or so) cleats of non-absorptive (plastic) material under the mounting flanges. The fiberglass insulation acts like a sponge and will hold water against the tank. The water will become stagnant and corrode the aluminum tank. This is much worse in salt water but often leads to leaky tanks in as little as a year or two even in fresh water.