If you modify "Been in the pen so long" to "Where have you been so long," you get structurally similar white-sung stuff from 1907 (TN) and 1909 (WV) that E.C. Perrow reported on in the 1910s, with a melody given. On the structure, compare "Going Away From Home" by John Snipes, who was born about 1900 and learned songs from musicians much older than himself. (Forgetting the structure, Howard Odum came across a version of "Railroad Bill" before 1909 that happened to have the lyric "Where have you been so long" in it.)