I cannot see how you would get that into frame rail, where? the back end of the rail? And you are right, I doubt that the floor sheet metal would hold up...even if you inserted a steel shim stock to press against, it seems like this tool would tear the welds loose. That's my take on this tool anyways.
I'm sure others have had to do some repair, and I will need to also so I'll try following this thread and see where it goes. I'm maybe thinking the "spot-welded" nails and possibly a bit of heat, but that might be for minor repairs I'm thinking.