Greatcoats are very bulky, and knowing how to roll (for external pack attachment) or fold (for internal pack storage) is a very useful skill. No manuals exist in the U.S. for the Civil War, but the assumption is the WWI (AEF) procedures are pretty close. Here is a YouTube on folding that shows two different methods... Enjoy!

https://www.youtube.com/watch?v=ZCqb6VRzXe0