Clamp a piece of copper behind the steel being welded,,
the thin sheetmetal will weld like it is 3/8" thick,,, (10mm outside the USA!! LOL!!! )
The copper is not consumed, use it over, and over,,
I have welded 0.060" (1.5mm) thick steel with 1/8" 7014 rod,, I am not brave enough to try 7018,, but, I think it may possibly work.
No crazy low amp settings,, actually normal settings work best, it helps to melt the rod quickly, so you can travel fast,,
Occasionally, I will get the weld to stick to the copper,, but, that is seldom,,
I have a mig welder for my Miller Trailblazer,, it has been in the attic of my shed for over a decade,, I even have 3 tanks of different gas types.
but, as long as I can get to the back of the part being welded,, I clamp a piece of copper,, and weld.
Most of my copper is about 1/8" thick, easy to cut, easy to bend, I do have some pieces up to 1/2",, I use when clamping to try to make the steel flatter,,
I even add hard face weld to tiller tines, using 1/8" rod (that is what Amazon had).
The tines turned out beautiful, the weld fuses to the steel, and just sets on the copper, no bond to the copper at all.
I can make a nice sharp, extended, tine out of the worn out old "stump".
I have done two sets of Troy Bilt Horse tines,, and worn out both,, I just purchased a third set last season,, pre hard-faced.
I will weld those in about 4-6 seasons from now,, if I am still gardening,,