Similar problems here. This is what I have done so far. The tailgate and steps of box, I used a DA, stripper pad and brass wire wheel on a drill. Worked great except for tight corners. Bought a small Craftsman gravity fed sand blaster. Hit all corners, then all prevously cleaned areas. WARNING- sand gets every where! Blast outside or spend a lot o time cleaning shop!
Then applied Dupli-Color Rust Fix (FOLLOW INSTRUCTIONS) After that used Dupli-Color Self Etching Primer. I like the results and have used this process (minus blasting) for minor repair on previous projects. 3-4 years no problems! I am NOT a Pro Auto
Body expert but this works for me.
