I welded studs to the back, made spacers out of 1/2" tube. Notice I even stud mounted the center of the "O". I'm gonna start welding studs on all my stuff if I can. Much cleaner look. I'd like to have a cd stud welder but they are mucho $$, even for a used one.
Every time I tried to mig or even tig something on the back you see the HAZ pop through the front. Then grind it down and even after sanding it sticks out.
I don't weld, i use a heavy tack. That helps. And then I sand with 120 on a da. They all come out for me. If you lay a bunch of heat to it it will create a spot that's not fixable. And I've seen 14g is about the limit. Any thinner and it's a bigger issue obviously.