Auto body repair & detailing: welding, propane tank, oxygen bottle

Question
Hi;
   I have a question regarding welding patch panels(rust-outs)on older type vehicles. I can arc weld thick materials like frames and such,but now i want to take a stab at mig welding. Recently i purchased a mig welder from a catalog which is a cheap piece for learning. It has a the ability to weld with gas and without gas.I heard that gas welding is much better for outer thinner panels,Is that true? What type of gas should i use? Do I have to use oxygen bottle with that or can i use the gas without a mixture?
                                  
                                            Thank you.

Answer
Hello Tom! Gas is preferable to flux core in every way. Flux wire is hard to weld with, requires more heat, and the welds are never pretty. A mix of about 70% argon and 30% carbon dioxide is pretty much the standard. Some use straight Carbon Dioxide, its cheaper. I've never personally use straight CO2, so I can't vouch for it's worthiness. You can get a smaller bottle you can trade in for just the cost of gas, when it's empty, for about 150.00, and it will fit nicely on a small welding cart. The smallest bottles, the type that are carried on portable welders, are a pain, not many welding or gas supply stores carry them. Those are just a little larger than a hand held propane tank. Happy welding! Bill