One of the best sources for research into the Southern States mission is the Southern States Mission manuscript history and historical reports, 1832-1964. I use it as a finding aid, since it really isn't a an original document. It is a scrapbook of sorts, collecting stories written in other sources about missionary work in the Southern States. Until recently, the only way to take a look a this record was to go to the Church History Library. Now, however, the microfilm has been digitized, at least most of it. Do you love pouring through microfilms? Well, it isn't the same. Few of us have an internet connection fast enough to get the same experience, but at least it is cheaper than an airline ticket. Have fun!
Update Feb 4, 2014: The CHL has changed the server this is on and the capacity for viewing the whole thing has tremendously improved. The flip side is that I have not been able to download entire volumes at once, only one page at a time. If anyone finds a way around this let me know.
You can also use the browse page the CHL has put together.