For the doors, I took off the door panels, sprayed a rust killer in there after cleaning off any surface rust and debris, let it dry ,then I sprayed inside the doors with a bed spray.
For the bed, I drill three holes on the inside of the bed sides ,sprayed inside those holes between the inside and outside walls with a rust killer primarily around the wheel wells used a Eastwood frame spray with the hose, I did the same thing with the rocker panels from the backside of The Rocker drilled holes and use rust killer and frame spray in there as well.