Yes, I'm using a MIG welder since I don't have a TIG welder. I am using 308L wire to weld stainless to stainless. If you're welding stainless to miid steel you would use 309L wire. Normally you would use a tri-mix gas to weld stainless (argon/helium/co2) but this gas has become very expensive so I'm using a new gas that PraxAir handles which is much cheaper (argon/nitrogen/co2) which they call STARGON

I decided on using stainless since I would need to use much larger aluminum to achieve the same stength and the cost savings weren't all that great. I also have an easier time welding stainless than aluminum.
Here are some good articles on the topic:
http://www.lincolnelectric.com/en-us...t-welders.aspx
http://www.lincolnelectric.com/en-us...al-detail.aspx
http://www.praxair.com/~/media/North...S%20P8785.ashx