as long as you dont have rot you should be find with sanding to bare metal, bondo, primer base clear.
Here are some "backyard" rot fixes I do lol.
1: Started as 4 little rust bubbles. THis is what it looks like behind.
2: Cut the area out more (used a small mirror to see the panel behind and cut beyond the rust.) Then I ground down the rust and applied por 15 all over the area and on back of the outerpanel. Waited till it was tacky to apply the fiberglass patch and bondo etc. (Let that set for a day before sanding).
3: This is basically the final product (with spray cans) No clearcoat was applied yet. But you can see how it comes out. I did the clear and let it dry for a few days before rubbing and polishing to blend it. It looks perfect.
Thats basically my redneck barn body shop. I did this on the rear fenders 2-3 years ago and the rust in those areas hasn't come back. But popped up in different areas. Cancer (rot) like this cannot be cured without new metal. But I try my best