I took one of the striker cover plates (not sure the regular cab trucks have these) to the paint lady at the local hardware store and had a quart of rust paint mixed.
Seam sealed the A pillars to the floor on each side last evening. I used a throw away brush and painted over the rust converter with my hardware store paint. Yeah there’s brush marks, but I’m not too worried about it. It’s soon to be on the underside of some sound deadener.