Back in the 70's we painted Navy ships and rusty military hangers with government red lead, which worked very well. Years ago I was wanting some for my Camino's rusty floorboards. Not feeling up to the intrigue of finding some or making it up , all I did was chip the heavy rust scale away, and give it a quick surface grind with a drill mounted sanding disk, followed by a wipe with a rag and thinner. While I did not expect results comparable to red lead, I took a leap of faith and bought a gallon of Rustoleum Rusty Metal Primer. The first full brush coat penetrated the surface rust, and the second full brush coat sealed the deal, by stopping oxygen absorption. The point is, no rust has reappeared after years of my doing this, and the paint looks as good as when applied, except for worn off areas, because I don't have carpets or mats. If I had top coated it with a compatible Rustoleum finish coat ,after the two primer coats, it would be even more impervious to re rusting , but I haven't even had to do this. I might, as it comes in assorted colors and sheens. It is important to wash all surfaces clean of salt deposits, and you must apply two full coats, with adequate drying time in between. I prefer brushing it on. I think two primer coats, alone, seal against rust better than one primer coat and a finish coat of enamel, which is the usual procedure.