How do you remove self-tapping screws from RV frame?

If you thought drilling the frame was difficult, drilling into a fastener will be another level harder. If it was me, I'd grind the screws off with a 4" grinder and drill in new locations for screws.

If you are having difficulty with bits, slow your speed down and put less torque on the bit. DEpending on what size hole you need, drilling a pilot hole can sometimes be a labor saver.