After you clean the rust by grinding and wire wheel, you can patch holes with epoxy. The easiest to access and use is probably Bondo. You can get it at auto supplies, and sometimes at building supplies. It is used most of the time to patch holes in sheet metal on cars. Don't try to just fill the hole. Spread it on an area much larger than the hole so that you can "feather it in" on the edges.
It is important to get off all of the rust, or get it neutralized. Sometimes a product that has phosphoric acid is helpful. It doesn't always seem to work though, so you may want to try a test area before doing it all.
After you wire wheel, grind, and patch. Then a good coat of primer, and a heavy coat of rustoleum paint should help you get some more years out of it. A word of caution... you'll need to let rustoleum cure for several days so that the liner will not stick to it. If you need it to dry more quickly, you'll need to look at either spray paints, or an automotive paint. I prefer rustoleum because it is very high in solids, so you can put it on heavy with a roller, airless sprayer, or brush. And, it holds up very well.
Al
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