[DanEC]

My car sits in the garage a lot but after about 8 years I haven't noticed any rust issues with the rivets anywhere and I typically used aluminum rivets with steel shank. The aluminum/aluminum rivets for fiberglass panels is probably a good approach but the aluminum panels ERA supplies are pretty stout and unaffected by riveting them to the steel structure.

The only painted rivets on my car are at the rocker where it rivets to the outrigger tubing. After riveting they got a bit of sanding in the body preparation phase but then were just primed and painted over. None of the paint has chipped off of them so far. I would probably prime everything at least one before installing the rivets and sand smooth and then install the rivets and do a final priming of the body over the top of them.