I like the fenders on the trailer but I had changed the springs and they were not OEM, so things were a little different, which wound up causing a fender issue. On this trailer the mounts for the springs are welded on a piece of angle and bolted to the frame. Which would mean disassembly of almost everything axel related and re-drilling and it's too hot to do all that. So I whacked with the grinder and remounted. That in itself is a pretty decent job in the heat but it went well.
The trailer is galvanized and if you know anything about that, it means it can be hard to weld. You MUST get all the galvanizing off to do so successfully. That means using the grinder to get to good steel. I welded it with the wire feeder and flux core wire. As hot as the little tinker-toy welding machine will go. Downhill. A novice might have tried uphill and it would have been a mistake in this particular instance. The cuts were slanted and beveled just slightly. So I tacked the top and got it level which give me an open gap so the weld would penetrate all the way. Very strong and a nice weld considering all the factors.
I hesitate to weld on a trailer because the heat changes and degrades the galvanizing around the weld zone. In this case it is in an easy spot to get to and easy to keep some paint on it to prevent corrosion. If you need to weld on a trailer you should keep all this in mind, although a trailer used in fresh water doesn't have the same corrosion liabilities as does one dipped in salt on a regular basis. Still, to weld it successfully and have a good product using one of those wire feeders, the metal must be clean of contaminants (galvanizing, rust, dirt). A stick rod (6010) is more forgiving but also carries much more heat.
A universally hated operation during my career as a welder of offshore wellhead production equipment. We would run and hide when a supervisor even looked like he was about to make that assignment. ;) Most of the handrails, ladders and deck grating came in H. D. galvanized and more often than not had to be cut and welded to fit the situation. No telling what I ended up breathing doing that, sure there must be protection for that these days.
But yes, grind it off if possible, weld it to fit your situation, and there is a product called Regalve that you can heat up the surface with a torch and melt it on. It is supposed to mimic the original hot dip and if it was good enough for the offshore engineers it must be good. Yes 6010 SMAW (stick) would be better, not a fan of Fluxcore but it got the job done for you. Living close to the shipyard you may have a source for a stick of Regalve. As I recall it smells every bit as bad as the original HD when applied, so maybe a respirator is appropriate.
Yes, not among the favorite operations a welder can get assigned to. I was surprised how well the FC did it. It welded like a champ for that little machine. I've been contemplating an advanced machine for the shop and ran across a deal on FB yesterday with a Miller plasma and TIG rig, and a TABLE. Waiting on word right now about it.
Hope you get your machine, I'm kinda in the market too. However, I'm not running any more power to my shop. I'm limited to 220V 20amp so a machine that will offer reasonable output at reasonable duty cycle with that max input. Probably one of those inverter units. Would be happy to run 1/8" electrode at max of 140 or so with decent duty cycle. Shop doesn't have a subpanel and a long way to the main, don't want to be resetting tripped breakers as a way of life. I don't expect the soft start and arc that I had with those Lincoln SAM 400 motor generators way back then, but then I don't think anyone uses them anymore.