This took some time and patience.  Getting the fit just right and figuring out the right setting on the welder for the thin sheetmetal took trial and error.  After the back and bottom seams were tacked, it was a matter of bending, hammering and trimming the other 2 edges and tacking them in place.  The seams were then welded completely.  It turned out ok and blends in well after the welds were smoothed out.