Hicrop10 , to paint the frame air tanks etc. I would recommend have sandblasted then use epoxy primer over the bare steel then apply your paint of choice . Let the epoxy primer dry for an hour before applying the paint I would not recommend using a primer surfacer like you use on body panels because that has to be sanded before any topcoat can be applied and offers very little corrosion protection using the epoxy as a wet on wet sealer is the best way to go . I use Axalta products in my shop formally DuPont. I use Montana epoxy then I use imron industrial paint over the epoxy. If you use PPG use shopline epoxy then use ALk industrial paint I have done this many of times over the years it works great and holds up extremely well