Stepside bed removal

[Chevyman680063]

Anyone have any tips on removing a stepside bed? I have the bed unbolted and the tailgate off. I wanted to take the fenders off before I tried removing it but the bolts/nuts are rusted together. I tried tightening the nuts to see if they would snap off but they just spin in place since the original bolts have a phillips head and can't keep the screwdriver from slipping off. You think I could use an air chisel to take off the bolt heads without damaging the inner bedsides? Thanks in advance.