Firstly i would get a copy of CKC,april edition i think had a good article from AshG on mig welding.
As mentioned make sure you have the earth clamp and torch polarity correct as it is opposite to using flux core wire.
Dont be afraid to try different power settings and gas flow rates.My mig is a 200 amp but only has 4 settings,i have found that the 2nd setting is best on the chassis with a gas flow rate of 10l/min as im indoors in my shed.
The best thing to do obviously is just practice on some box section not straight on the chassis.Once you get it right it will sound like bacon sizzling in a frying pan

.Strange i know but when it happens you will know.