boxorox, if you want to learn to weld sheet metal with a stick welder, get you an old 55 gallon metal barrel, preferrably not rusty, and cut some parts out of it to practice on. If you got a thin enough blade to cut it with, you can make some simple slices and then weld them back up. It's best if they do touch though, so removing them is best. Practice. Once you get that barrel mastered, then go fix your fenders.
I looked at your thread where you mounted the hitch to the front of your tractor. I see your welds look like "laying dimes". Like you took a roll of dimes out of their wrapper and layed them down, they lean but go in equal increments. When I first started welding a welder taught me how to "lay dimes" and I taught myself from there. You got the dime laying going on, the basic circle action of the rod. You just need to learn about materials and heat ranges.
You have a good general purpose stick welder. Those old lincoln tombstones are hard to beat for a basic welder. I have an old Marquette, about 35 yrs old, I uncrated it when it was new. Another good old basic welder. I basically weld at 90 degrees for 1/4 inch material using a 1/8 rod. I adjust my heat up or down as needed for the thickness material I am using and size rod I am using. I do a lot with 6011 rods, if welding mild steel. You've got it going on you just need a lil practice. Get you that barrel and master the thin stuff. You can do it, practice.
If using a 1/8 6011 rod, turn your heat down to 60 degrees. The lower the heat the more your rod will want to stick but 60 would be best. The more you hold your rod away from your work, the more heat you create. Keep your rod as close to the work without it sticking. And practice. You'll burn some holes, but you got a whole barrel to burn holes in. You'll learn how far you can go before you do burn a hole and you'll get better. Don't try to make a long solid weld, do an inch or so and get out of there, let it cool for 30 seconds or so and go for it again.
If you got a 1/16 rod it would be better but I do most of mine with 1/8.
One night a buddy and I were drinking a few and one of us asked the question, IF we had to make a small repair and ran out of rods could we use a coathanger to weld thin material using a stick welder. He was a professional welder, 2nd generation welding shop owner. He said he didn't know. So we got a coathanger and cut us a rod length out of it and proceded to weld up two barrel pieces from a scrap barrel. It worked, not as good as welding rods, but it did make a strong weld that would have worked if needed. But it also took someone that knew how to weld thin material to do it.