Other than copy and paste a reply in progress to some document on my PC, is there a way to do this internally within thirdgen.org?
My apologies if I've the direction somewhere.

 

There is no area or management of Drafts.

However, it does auto-save a New thread or New Reply, periodically, to your browser's limited storage area. If, for some reason the post is lost, you can return to the thread (if a reply to existing thread and post) or forum (if creating a new thread in a specific area) and if there's a saved draft it will show Restore Auto-Saved Content below the message area.