Rusty bolts

so I’m working on a 72 truck bed trailer and restoring it to turn into a camper of and the bolt head for the mounting plate snapped off and I’m trying to get it out but even sitting there with a sledge hammer I still can’t get it out I was wondering what do y’all do take care of rusty bolts or metal that doesn’t want to come apart ?

If you have not driven the bolt t where you cannot weld a bolt to it you will have to pick up the bed to cut the bolt just above the frame then drive it out.

This is my go to for rusty bolts. I let the bolts soak in penetration fluid then I hit it with the air hammer and twist the adapter with a wrench. This in line hammering seems to loosen the threads up better than the rotary hammering that a traditional impact has when the rust has seized the threads. You can find these adapters on amazon for cheap.