Came across an interesting account(p.208-210) of an escape from the prison in Mamie Yeary's,,"Reminiscences of the Boys in Gray." Not sure if your aware of it as the massive old book writtin in 1912 from interviews with soldiers in Texas is not indexed.

Account was from Young C.(Tobe) Edmondson,Co.G,Colonel Turney's 1st Tennessee Infantry,Archer's Brigade.He was captured at Gettysburg. Tobe says he floated off on the night of Aug.12,1863 along with his crew:Tom Stewart,John McKinney,James Cashion,George Stonebreaker and John Moore.

MWT