I have just begun the restoration process of my tiny fiberglass trailer. When I pulled the interior lights down off of the hull, there were multiple rivets that were holding them in place, that now needed to get removed.
I gave each rivet a good tug with a pair of pliers to make sure which ones actually needed to get removed. (all of them :P)
I figured out which of my drill bits was the same size as the hole in the rivet, and then used that bit to drill out the rivets.
1)Assess what size drill bit your rivets will need.
2)Drill out the rivet
3)Patch your hole (I'm patching this fiberglass hull with a 5 minute quick-set epoxy, the holes these rivets left behind are very small)
If you have questions, feel free to comment.