We welded the top plate in the trough and on the ends. To connect the top plate to the vertical face of the frame, we cut and formed another plate from 12-gauge cold-rolled steel. A plug weld looks good, but its main purpose is to add strength. Note that multiple tack welds were used. This piece had to be formed a little at a time, and tack welds held the edges in their final positions while the next section of the plate was tapped into place with a ball-peen hammer. Final welds were torched in after the forming and tacking was completed.