Depends, do you care about your repair from a visual standpoint or just a structural one? If you don't care about how it looks, just so long as it's safe and structurally sound, you can cut/grind out all the rust, make your repair section and weld some steel plate over top, similar to what the safe-t-caps do. I've done this before on a few vehicles. Done properly, your repair while maybe not visually appealing, is perfectly safe and structurally sound.