With any flux core welder, make sure you have really good ventilation where you are working. The flux (coating on the wire) gives off some pretty noxious fumes along with quite a bit of spatter. They are a bit messy to work with but will get the job done. Just do a fair amount of practicing on metal the same type & thickness as what you'll be working on. Once you get the settings right (heat & wire speed) then you have to also find the right speed for your hand to move. With sheet metal, you need to be careful how much heat you put in any one area. Begin by tacking small spots around the workpiece and alternate where you put them. Kind'a like the way you alternate torquing down bolts. Just take your time, move from spot to spot and fill it in slowly. There are tons of tutorials online.
One more tool that is handy for this kind of work is a set of "butt weld clamps" to hold the metal flush until you get it tacked. Cheap and handy...like these...http://www.harborfreight.com/8-piece...mps-60545.html
Magnets are handy too.
Best of luck on the build. Once you begin welding you will likely start coming up with all sorts of things you wouldn't have otherwise.