Help spinning nut in frame

Was changing out my rusty crusty gas tank straps and one of the bolts came halfway out and then started spinning. Of course I can't access or see what's going on but I'm assuming a nut welded to the frame broke loose. If I cut the bolt, what are my options for a new bolt for the strap? Would a rivnut work?

 

I've had rivnuts on 2 of the bolts for my gas tank skid for the last few years with no complaints. Only thing I'll say is that I had to use a dremel to clean up what remained of the weld from the weld nut so the rivnut could compress properly. Also painted after dremel but before rivnut to try to prevent future rust. Took a little bit of time to get right but it has held.

 

I ran into the same problem when removing the tank to replace my fuel sending unit. Check out this thread.