It's easy to do a cartoon southern accent. To make it authentic, you have to have a good ear and willingness to practice and know what to listen for.
Four good examples come to mind: the wolf from the Droopy cartoons ("hey, man"), Foghorn Leghorn, Pappy, and Elvis (the last 3 from Looney Tunes). Foghorn was modeled from a Southern senator, I think, but was understandably exaggerated.