Hey Bill,
I'm new to my AS, but would it be any different than installing a new roof vent?
As I took apart my
1963 Sovereign, I found that the water heater, furnace, water fill pipe, and antenna mount were all done the same way, I believe at the factory.
In all cases solid buck rivets were used with putty sandwiched between the outer panel and the mounted piece of aluminum.
With the after market replacements and add-ons (roof vents and A/C), the putty was also used, but screwed or pop riveted. These leak wherever fasteners let go or did't catch. The factory installed stuff did not leak.
I've read about Olympic rivets, which are blind structural rivets which don't leak (apparently), but haven't tried them. Perhaps others have.
Rob