You can double film it and run a blower that causes a wide area between the two layers to insulate in the winter. I realize I'm not using all the proper terms here but greenhouse megastore has videos online on how and why to install it. I'm in 7b and my biggest headache is keeping it cool enough to keep anything alive over the summer. Listen to the advice to do it right from the start, retrofitting is ridiculous! I do dearly love it though! Best of luck!
