Are you planning on sanding? Rust is a nasty beast up here. I have been sandblasting a '73 SS El Camino for 2 weekends now and though you may think that's extreme, you'll be doing the same in time if you dont remove the rust before you paint. Even the rust inhibiting, or cold galv. paints require the rust to be removed(at least the bad stuff). Rust-oleum makes a rust reformer thats great for utility areas, but it leaves a texture that may not be suitable for a finish area. If you dont remove the rust it will come back and by that time it's pitted up good. I was told the best setup is clean bare metal and a self-etching primer. And as far as I know, sandblasting or sanding/grinding is the only way to remove ALL of the rust.