The corner is tricky if you get too impatient. Make sure when you weld anything with thin sheetmetal that you wait in between the welds. If you look at this weld, I started at the bottom with a tack and then tacked the top. I then moved, welded for an inch, and moved on to the other side, so that the metal had time to cool. If you don’t wait, the metal can warp and move the bed so the tailgate does not line up.