thanks Peter and cb. wherever I clean with a wire wheel, I follow up with POR's degreaser and then phosphoric acid. And POR paint, couple coats at least. My car needs a paint job, just for how it looks, and when I get past a couple mechanical problems, then I will be dealing more with the rust and paint preparation. The Fluid you mention looks like a good thing to use after paint, to prevent future rust and maybe stop what is hidden. I will get some after paint and use it in those narrow places and places I can't see.

By the way, what I did with the rust down in the tight places was to clean and poke and scrape as best I could with various tools and picks. And then degrease, phosphoric acid, and POR paint. I dribbled the paint along the top of the opening and then blew air down in there to minimize puddling. I also used the air hose while degreasing, to try and remove what I could. End result (that I can see) is pretty good, with four small holes that go through the metal. I am looking at fiberglass tape for those, and maybe bondo. Better ideas are welcome.