Krylon makes a chemical in a rattle can, not too bad. Rustoleum too, and there was avalible in a skim milk like liquid (white and THIN. years ago a friend had a gallon milk jug of stuff that he got form an airplane mechanic. We painted it on most sides of swiss cheased floor in a 60 ford sunliner, one that would nearly move in the breeze, and it turned the rust black, and in about an hour you could STAND on that floor! I have been searching for that chemical ever since....

POR can be sprayed, but it has very very specific handling instructions. It also goes a LONG way.

I made the mistake of putting it on the outside lower part of my doors, and now i have to sand it or fill the edges where it meets the untreated metal...can't paint over the ridge...live and learn!