Based on my experiences flux core wire will not work and stick welding will not work for sheet metal. I know that's not what you want to hear but if you would do some searching on the internet I think you will find that what I am saying is valid.

I recall seeing that Eastwood had a device they called a "stitch" welder that used 1/16" rod. The device fastened to your arc welded and allowed you to weld sheet metal. I can't vouch for it, but since you asked, that's the only stick option I have ever heard of for sheet metal. Even using 1/16" rod is to big though for sheet metal. http://www.eastwood.com/stich-welder-welding-quarter-panels-with-the-new-stitch-welder

And based on this, it doesn't sound like Eastwood's device works either: http://autobodystore.com/forum/archive/index.php/t-15005.html