Cotton Pen where Bayard and Ringo Sleep (Location Key)

The pursuers in "Vendee" meet Matt Bowden for the first time at their campfire beside a "cotton pen where we were going to sleep" (103, 166).
I don't recall another reference to a cotton "pen" in the fictions. Here the word almost certainly refers to what is elsewhere called a 'cotton house,' a rudimentary shed that was used to store cotton after picking; except at harvest, these were empty.