Are these the fine thread guys with a drill point? It was all I could do to remove four that were holding a battery rack together. If you have a travel trailer frame, steel around 1/8" thick, you might get them out with a penetrant soaking, and I like to beat on the ends. Seems to jar the threads loose. I have not tried this, but for those that still have heads, I wonder about an electric screw impact driver, like you'd use for wooden deck boards.
The things are hard hard hard and meant to be driven with a power tool at about a million RPM. We have some through our Ford E450 chassis that's 5/16" thick. I have NO expectation of doing anything with them but leave alone or break off.
Based on recent experience with HF "nitride" drill bits, the screws are tougher than any HF bit or extractor.
