This tank bottom is vee-shaped thus any debris or crud winds up in the vee. The tank bed was very well designed and the vee is suspended in air on all sides so no moisture was in contact with the tank.
When we cut the tank open I sifted thought the dead organisms and found a chunk of dissimilar metal right over the hole. It seemed to possibly be a piece of stainless steel that had somehow fallen into the tank somewhere along the way, possibly during a sending unit change out?
I suspect that this piece of errant metal was the cause of the pin hole. There were no other signs of corrosion despite this being a 31 year old aluminum tank. Canadian Sailcraft did a very good job designing & engineering the fuel tank & beds.