I have to admit we have never welded one in either. Being a 12 year Master Tech for Ford Motor Company and knowing how differently the box flexes from the body, I would definately not want to weld the two together. We usually loosen the bed and slide it back (no more than 8 torx bolts most of the time) to make plenty of room, then run a silicone bead on both ends of the seal, screw it into the body and the bed, seal each of the screws in also, then slide it back together. I have NEVER had one return with a leak. This method was suggested by our wholesale rep at Topper King in Brandon, and it has never failed yet!

And yes, this is Land O Lakes where rednecks double their pickups as submarines!