With this issue, it does not matter what level of resto or the use of the truck. You gotta have a good solid floor. The first step is to leave the trans cover on but take off the gas pedal. Aggressively wire wheel the whole floor down to bare metal. Survey the floor for thinness and holes. Report back with pics and description for suggestions. There is only one way to fix floor rust out and that is with welding a patch or three. A pin hole will always have a larger thin area around it.
The trans cover can be removed after, for more wire wheel under and repair if necessary.
Always wear eye and face protection.


Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn