Here’s where the box stands as of last night. I put weight on the cage to set it in place, then tacked some scrap metal to the open end of each bottom bar. With both bars at the proper angle, I measured and cut two legs to meet up with the ends and tacked them to the top bar. After checking that fit, I brought the whole assembly inside and welded it all up, as well as added two sections along the bottom side of the short edge. I closed up the holes on the bottom ends and smoothed the welds out on all of the outer edges with a flap disc.