Shop I used to work at had a Snap-on spot welder that worked nice but sometimes can be difficult to put the "c" around odd shaped panels. So typical we would drill out old spot welds with a spot weld bit and mig the new panels in place through the new panels hole. Most Bodymen I worked with also used this method more mostly for efficiency, U would usually have your mig there anyhow so dragging out 2 units was kinda overkill but if you are looking for completely factory looking spot welds they do work nice.
