What I did
First, I sanded the flanges as flat on the mating surface as i could get them,then made sure the flanges were uniform in width (1/2" or so) and radiused nicely on the edge , then drilled #40 holes every 2" and countersunk. I then attached to the aluminum fuselage structure with Proseal and clecoes only, letting the sealant cure for a couple days. While sealant is still soft, use acetone or MEK to wipe the edge smooth. The Proseal will paint fine. After the cure, I installed what are refered to as "A" rivets (annealed soft alum rivets), then just primed and painted with the rest of the plane. If you try to feather fill them, there is a likelyhood of cracking through the paint, though some have been succesful. Mine look riveted on, but you cant see the rivets or any bulging of the flange...the trick is in the Proseal.
