#ONE, use all aluminum rivets. Many pop rivets may have an alum body but a steel mandrel [pin, nail, center, ect.] bad news. Buck rivets for anything structural, pop rivets for interior skins or light duty connections. Most everything is 1/8th inch dia. holes. Carefull on the drill out, use a 1/8th bit, don't "oval" the existing hole. If you do you may have to re bore up to 3/16ths and use a 3/16 rivet. Research & use the proper lenght rivet for the thickness you're joining. To long, loose grip, mandrel can break off long. V.T.S. is a V good supplier. Aircraft spruce is great for alum and rivets. Order a catalog from jay-cee sales & rivet supply, lots of useful info, Rivets by Jay-Cee | Rivets In Stock - Rivets & Rivet Tools
. Be prepared for "spinners"' you bore and the rivet spins. If you angle the bit you oval the hole, you spin long enough you wear the hole. Either way you re-bore to 3/16ths. A thin sharp spring steel putty knife with the blade all the way through the handle will shear those off nicely with moderate hammer strikes, tap the body of the rivet through with a punch. Heads up on a drill. Probably the best tool I bought was a common cheap 1/4 inch variable speed 110 Volt drill. Light and easy, for this application way ahead of the "better" 3/8 or 1/2 inch loaded with options! Buy a box of 1/8 bits. At the first sign of wear use a new bit. Worn bits have a nasty habit of walking off center and screwing up a hole. Sometimes around hatches, doors ect you will find a small crack in the skin. You can use an aluminum backer on the back [small washer made for this purpose] to stabilize the problem. No need for concern, odds are if you hit a snag someone here has before you and they have a solution, just ask.