9 The bottom boxing plate is the last piece of the puzzle. Line it up so that it is parallel to the inner boxing plate, leaving a gap for welding. Tack weld it to the framerail and then completely weld it to the inner boxing plate. The outer edge of the bottom plate has a pre-cut profile showing where the stock framerail needs to be ground back to match. Grind the framerail lip back to this point and then weld the framerail flange and bottom plate together.