I've read lots of advice to the effect that an aluminum tank must be
mounted so that it doesn't stay wet. I've seen suggestions for
glueing plastic stringers to the bottom to support it, for example.

My tank is in side of the bilge, and is thus triangular in athartship
cross section. It rests on the lower edge and the upper outboard
edge.

I'm wondering if it would work to cover the whole lower edge in
fiberglass epoxied to the aluminum. I would think that would keep it
dry and give me a good mounting surface.

Any thoughts?