I have an air operated rivet gun but of course that requires having an air compressor. I also have a few different hand rivet guns. It has been recommended to use 3/16" peel type rivets in
fiberglass as they spread out the load area. Our
Uhaul is similar to your
Burro with a double wall / inside shell. The space between inner and outer varies so be careful when drilling. Either wrap tape around the drill bit or some kind of tubing slipped over to limit penetration. A number 11 or 12 drill makes a hole slightly larger than 3/16" so it is easier to insert the rivet. I installed my
awning rail with rivets, but that's a whole other controversial topic that I'll avoid here