When it comes to the battle against rust, there is no permanent solution. That being said, use a sander, with something around a 60-80 grit surface to remove ALL of the rust. If you don't get it all, then you're wasting your time. The lower the grit the rougher the surface, and the more metal/rust it'll shave off the surface. Once you've got it all, switch to a higher grit to get a smoother surface. And once that's done, find the highest grit you can, preferably 400, and sand it again. If you go straight from 60-400 you'll wear through the sanding paper before you wear through the metal, so you have to make it gradual. Once you're done sanding use a rust-inhibiting primer to completely cover the exposed steel. The number of coats will vary, but it's better two have a bunch of light coats than one thick coat. Once everything is covered with primer, use a paint-matching finish coat, using the same method above. And finally, apply your clearcoat. See? Easy.
