Thanks, dapepper9 I am not great at welding, but do have a Mig welder at my father in laws. It is a work truck, does not need to be pretty. Just needs to hold up and slow down the cancer.
In that case, get yourself a random piece of 20g sheetmetal or a panel from a junk yard, cut a pieve off and weld back to kinda figure out what settings you need and hand speed. Small rectangular piece of 20g a little bigger than the rusty area once the welder is figured out, cutoff wheel to remove the rust, weld in the patch.
Feather out the area of the paint with a sander, body filler to make it one smooth surface, primer, paint, clear.
Sounds simple but it is labor intensive. However, doing work like this on a tailgate is an easy way to kinda gather materials and know-how for the next spot that appears. Cheaper than going to a shop too