HELP! Bed rail bolts and nut replacements

So I stripped 2 stock allen key bolts that hold the tie down rails to the bed side and snapped another one while removing my tonneau cover in prep for a softopper. I have been looking the around the forums and it looks like the bolts are M6x1x16mm bolts. I was planning to replace them with regular hex head bolts to make them easier to remove/replace in the future.

My main question is the one I snapped it sounds like the nut behind the wall is twisting with the bolt. What connects these behind the bed wall and what is the replacement for one of these nuts? Is there a way to pop the bed side cap off the top and get vice grips down inside to hold the nut in place to back the bolt out?

 

Yea… pretty much what I’m finding too