Ernie,
I do this on a regular basis in our sign shop.
While we don't powdercoat, there are several things
that can make this a lot easier.
First,I wouldn't used bucked rivets, one slip and oops..

Prep the panels per your idea and use either
1) Lord adhesives epoxy (check their chart for proper one to use,
I'm sure they make an adhesive that will tolerate 500 degrees for the
short time it's in the oven.

2) 3M VHB tape. this is what we use for 99% of our signs and after it
reaches ultimate strength (about 48 hours) I can't get things apart
without seriously damaging either piece.


erie