I saw that the pickup tube was starting to have pin hole corrosion, but as per my diesel and this tank - I notice generally corrosion happens at the waterline. I don't believe at all that the uncovered top of the black water tank will corrode first. It will be the bottom or the sides, thus my lack of 100% encapsulation. So my prediction for the failure mode will be pinhole corrosion on the pickup tube (epoxy glass wrapped up almost to the top of the tank on the inside) and then at the 'water line' on the sides of the tank. Then further pinholes etc. With 2+ layers of fiberglass, I think there would need to be a loss of >20% of stainless before structural issues occur; and predict that the pickup tube vacuum/structural integrity will fail first.
I have read that stainless doesn't like being submerged, however I am less familiar on how a covered 'outside' of a tank would affect an unchanged and uncovered 'inside' of a stainless tank. It doesn't intuitively make sense to me that a covered/uncovered outside portion of a tank would affect pinhole corrosion on the inside. I don't claim to know either. I'm sure however that...we'll find out! But we will have to wait. As dlj said, probably until I cross the pacific