Looking for a little help on a spinning fender bolt
 

Doing a tear down of a 69 Camaro that is super rusty. When I went to take the top drivers fender bolt out (the one behind the door when its closed). It started spinning about half way out. :(
I looked in the assembly manual but I can't tell if there is anything accessible on the back side of this bolt. or if this is something that's going to require welding work to repair. I will find out eventually when I start stripping the dash out. But I was hoping someone here knew. PIc included for reference of what bolt i am talking about. Thanks in advance for any help.
https://cimg8.ibsrv.net/gimg/camarof...3c0022e896.jpg

I did find out its a caged nut that is enclosed, sounds like the only way to repair is to cut a hole, weld in a new cage nut and seal it back up