GM Accessory Auxiliary Step - install question

[DeadheadNM]

I'm leaning toward installing these GM accessory steps in the blazer I'm building before the rocker box end plates are bolted on. These steps would make it a lot easier for my wife to get inside.

Am I correct that the rivet/well nuts provided mushroom outward when the bolt is torqued down to secure the threads into the sheet metal of the rocker box floor?

I'd like to have a more permanent thread addition that would allow me to unbolt the steps when/if I choose to do so. Any ideas?

I'm concerned the supplied threaded end would loosen then spin precluding bolt removal.