Of all the 'miracle cures' for rust, RC800 is amoungst the best, but also amoungst the most expensive! We used to sell Dinitrol and I've used their body wax with great success. Lasted years. But it never sold well because of the price and at the time is needed compressor to inject it. Now they offer it in aerosols.
However, the only way to totally 'cure' rust is to cut it out and replace with fresh metal.