The stainless brush should be used only on your aluminum and not get contaminated with any other uses. MIG is good for thicker aluminum but requires at least a teflon liner or better yet a spool gun. It runs hot and fast and requires a push technique for gas coverage and a big contactor to work gap as it is actually a spray transfer process. TIG is good for control and thinner materials. It is a bit of a head game as you have to break through the oxide and make a molten puddle to get it going. Once it is going it really crackles and spits as the magnesium alloy in it burns. There are some good tips and tricks on these at the miller web site.These first two make too much heat and distortion on your freshly hand beaten body panels. For that you need to braze them together with a flame and flux (or flux core) and rod. There is some awesome Cobra and other aluminum car stuff as well as good information on the tools, tin knockers links etc at
http://panel-craft.com I didn't mean to make it a sermon. I just happened to be trying to dial in a spool gun at the moment. It should be worth it and save me a lot of TIG time on a big job I'm doing. Good stuff ain't it!