You may have noticed that on the outside of the cab wall the overlapping metal was not welded. It is not necessary to weld this portion. Instead, it is screwed together and seam-sealed using self-tapping screws and flexible seam sealer. You can pick up the seam sealer from any body shop supplier. The seam sealer is first squeezed into the gap from the inside of the truck, and then the cab wall is screwed together.