How are you going to get the welder tip around the top rails, and into the folds of the lower rails?
With a U-Bend laser-cut flat, you could do this easily. Fold and weld the top rails, locate and weld the lower rails, the fold and weld the bottom bends.
With any other flat, this will be impossible. Well, it will be possible if you build a super complicated, multi-layered internal block that will clear the rails and dimples and still be able to be removed.