you can remove rust mechanically, chemically or with electrolysis if you can get the whole part in a bath.
Phosphoric acid based treatments convert rust into black iron phosphate. Works real good on getting into the pits that blasting doesnt get all of.
Tannic acid products look sorta purple and leave a thicker film when theyre done. I dont really like these as much myself.
-Anything- you apply to steel is only as good as how well it covers the -entire- part. any chip that exposes the metal allows water and oxygen under the coating and allows the process to start all over again.
Id do all your repairs, and use fluid film inside all your rockers, cab corners, fenders and undercarriage if you live in the rust belt. search online if you want to try it out. I think I paid like 50$ a gallon? I forget. It looks like custard and smells kinda like peppermint. use an undercoating gun and a flex wand to get inside panels.