True North wrote:
Some of y'all seem to be forgetting that a major contributing factor is
the paint under the snaps.
The natural aluminum does a better job resisting.

Is not the paints fault. Is the aluminum that has electrolysis. Some
alloys, the 50xx, are much better at not corroding in salt water. Very
little copper content. Problem is the the 50xx and especially the 60xx
alloys do not bend and form as well as other alloys. So if you have nice
compound curves in the aluminum, may be a higher copper content alloy.