I have had some luck with rust converter. I'm not talking about body rot, just surface rust.

I had a spot about 2 square inches that was bubbled up under the paint on the right front fender of our '88 745 GLE. I scraped off the surface rust and wire brushed the spot clean. I applied the converter as per its directions, let it dry for a day, then painted the spot with touch-up paint.

three years later, the spot looks the same, not great, but no more bubbling.

You could try a course at a trade school, our regi9onal trade school holds many evening mechanical courses such as welding, body work, small engine repair, etc.
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96 855R, 95 855,854, 90 744 Ti - 340,000 Volvo miles put on 7 bricks