I have a 12' x 22' shop. It started out as a 12' x 14'. When I added 8' to the length of it I cut out a doorway which is about in the middle. I have the old part, the 12' x 14' insulated on the walls and ceiling and have a window a/c unit in it. On the doorway separating the two rooms I have a clear shower curtain, it may sound funny but there is a 20° difference between the 2 rooms.
I know that my "rigged contraption" doesn't help you in your situation, but it may give you some kind of idea.