I made one of these to attach to my Mig welder tip. Works brilliantly! You put an earth on the panel to be shrunk and with the carbon electrode draw a spiral shape with the power on onto the area to be shrunk. You may get a bit of sparking. Can also quench with an air line or even a damp cloth.
perfect way to remove a stretched metal dent from a panel.
You don't need an expensive machine to to carbon heat shrinking. If you already have a Mig welder and a lump of brass you can make your own!
http://www.mig-welding.co.uk/forum/showthread.php?t=7433
Definatly no trigger, however the carbon rods work.. And my god does it work! You place the rod on the panel and about 1/4-1/2 second later it arks and it has what seems like a 3 second timer, no sparks, mess, nothing, 100x easier than the way I've been doing it for years!