For the rusted part of the frame rail I am planning on cutting out the lower rusted section. Then sandblasting inside and out the best I can followed by epoxy primer and paint. Im going to epoxy primer and topcoat the cap too. Where the weld bead is gonna be I plan on using a SEM weld thru primer.
For the torsion bar its pretty much the same except to clean out the sand from the inside since the bottom is not rusted that much. Then spray either cavity wax or Eastwood internal frame coating inside the cross member.
After that I will use some sort of oil under coating on the inside of all the frame rails and cross-members. Still experimenting with some different types of internal frame coatings and oils for undercoating. Once I sprayed the underside of a truck with rubberized undercoating and then sprayed hydraulic oil over that and it ate the undercoating and it all fell off. Trying not to repeat that failure :)