shielding gas will allow for thinner metals and smoother welds but considering its body work sheet metal your going to have to grind it either way so really for sheet metal work it dosn't matter alot a cheap 110 flux core will work just fine if you do get a cheaper harbor freight other company one keep in mind enough money to buy a proper helmet most of the cheap ones only come with a hand held face shield and you need both hands for a decent weld
