[Nyle]

I'm going to second the rivets option. We've been using gussets and rivets for a while to build our robots and it's worked quite well for us. They're very fast to install, just as fast (if not faster) to remove, and pretty much always just as strong.

We have occasionally used bolts to hold things together during construction, or to allow assembly/dis-assembly in situations where a drill/rivet gun may not be available; when we do this we usually have the bolts go all the way through to the other side of the tube and use a nylock nut to hold it all in place. If you do want to have a bolt to allow quick dis-assembly, be sure to either buy bolts at just the right length or be ready to cut down bolts to size—it'll make assembly/dis-assembly significantly faster.