If your welder is new enough i'd speak to the store you got it from. I'd be returning it to get credit against a larger machine that is designed to do what you want without any 'add-on' and afterthought 'kits'.
People minimize what they want to do and make it seem easier than it is. 'I just want to weld body panels', thats' easily said and on paper the welder you purchased has the power to weld .022 steel - an engineer has calculated the requirements to provide the right amount of current to join steel of that thickness. What he didn't include - this is the expensive part - is the sophisticated circuitry to have control of the current at very low settings. Anybodies machine can weld 1/8th inch - nothing sophisticated there, right? A machine that can weld aluminum beer cans together takes a fraction of current that your machine has, but you can well imagine the sophisticated circuitry and control that the machine must be capable of to strike an arc and weld beer cans together.