Rust Neutralizer

My personal favorite is POR-15. Paints over rust and penetrates and seals so the rust is stopped in its place. Surface MUST be free of grease and oil or it won't stick. If its applied correctly its permanent and takes a grinder to get it off. About the only chemical that will remove it is paint stripper. Underside of my son's '68 Dart is covered with it. Inside of the frame rails are sprayed with Eastwood Interior Frame Coating, which sprays in with a long tube with a nozzle on the end.