Originally posted by: Oger
Anytime pal, to truly weld sheet metal correctly you should be using a TIG welder

, these are the ones you see OCC and any respectable shop using, they confine the heat to a very confined area thus preventing warpage, they also use a high frequency pulse through the tip thus making the weld extremely strong and non-porous.
If you happen to have several grand laying around, pick one up


I forgot to mention that the Lincoln Weld Pack models come standard with flux core wire thus negating the need for a shielding gas, this makes it easy to weld but it leaves behind slag which must be chiiped off before painting, also these wleding can be converted to gas shielding by purchasing a kit for about 100 clams, you reverse the polarity of the welding (instructions included), attach the tank, regulator and hose and off you go.