Allot depends on where the panels are.
If on an edge (like the inner fender panels) you can make a small press, use a real spot welder or I use a modified set of vise grips.
If there is an access problem then you might have to rely on the filler and pencil trick (can use a sanding disc, paper hole punch and attach it to the pencil also)
Make sure to add some deflection in the metal - too telling (that its been faked or added) when the panels are all smooth and flat. Normally th ewelder was ripping the big heavy tool away from the panel heading to the next one before it released or rested the machine on the car.
Have some pictures but will have to wait until I can get at them