Audi has been manufacturing a galvanized aluminum car (the A8 and S8 for the
last 8 years or so). Acid rain, or just plain old "rain" as we've come to
know it today, can destroy just about anything given enough time. So IMHO
it's a non-issue in this respect.
Most paints for that type of application are regulated, highly toxic,
generally not available at a home-depot type store, and very expensive. I
still say, not worth the hassle. Aluminum is one of those surfaces that
needs perfect prep, perfect application environment and still does not last
as long as traditional rust paint on steel applications.
I did try one of those "comparable" paints (don't remember who it was
made by, but was not cheap) when I ventured into repainting the aluminum
siding at my cottage 3 years ago. I followed directions to the letter and
waited for the perfect day. The results looked mediocre at best. Today, I am
looking into vinyl siding. All my effort has yielded flaking, bubbles and
cracking whenever you put pressure on a spot on any of the slats. No....I'll
never paint aluminum again.

B