Aircraft Spruce and Specialties (
www.aircraftspruce.com) sells a device called a "Cleco". It's harder to explain than it is to show, so I'll not try and confuse you. They have an excellent help line and can get you on the right track. Clecos are used to hold pieces of sheetmetal together while riveting. The washer trick above is very creative.
On a plane, if you need a flush patch out in the middle of a wing (for example), the best repair is called a "Dollar-dime" patch. Your hole in the skin is the size of a dime, and the backer is the size of a silver dollar (not a S.B. Anthony or dollar bill). The "dollar" is riveted to the backside and the "dime" is then flush riveted to the "dollar" as a filler. Clecos hold the whole thing together. You remove the Cleco and install the rivet in the hole. You could subtitute the rivets with stitch welds around the filler and remove the backer if it were brass or copper. Of course any size hole can be repaired this way not just "dime-sized" holes. If you think that was long-winded...ask me how Clecos work.
Stop by your local small airport and ask around for the shop that does sheetmetal repairs on small aircraft. For a cup of coffee, most any sheetmetal guy will show you what I'm talking about along with a bunch of other tricks for sheetmetal repairs. You'll probably find the best TIG/MIG welder in town there too. FAA cert. for welding is no laughing matter.
Good Luck on your project. I hope this helped.
