Manny, your boat looks a little different than my '82 cuddy, but still very similar as well. I did not have anything around my tank but foam and the two braces across the top.
Titan, these tanks are absolutely problematic, but not all have the problem. They are aluminum tanks surrounded in open cell foam. Once water gets in the foam, it stays there. The foam holds the water against the tank for years and corrosion sets in.
One of the causes I think is the way the boat is plumbed to get water from the cuddy and the front of the deck to the bilge. There is a 1" PVC pipe laid across the bottom and through each bulkhead - 1beneath the cuddy door, 1 forward of the fuel tank, and 1 behind the tank. The holes where the pipe passes through the bulkhead did not appear to be sealed in any way, (much like the holes drilled through the stringers against the transom to allow water into the bilge that may have snuck in through the rod holders??) Very poor and lazy design, IMO. As we know, water takes the path of least resistance and always obeys the laws of physics, so it eventually rots out the bottom of the bulkheads and gets into the foam. This was what I found on my '82, anyway.
Another problem that I found with my tank was the fill inlet. The clamp was too heavily tightened to secure the fill hose and I believe it pinched through the rubber, exposing the wire inside. As the wire corroded, it rubbed against and corroded the underside of the fill inlet to the point where there was a large hole and that was the primary source of all the fuel I smelled when I refueled. Escaping fuel also settled into the foam from this source, so I think my tank was in worse shape than most.
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