I hunted in Northern Minnesota this year, even though I'm from OR.. A BIG weather change. I found that either wrapping the heated foot soles they sell inside a neoprene cover or hand packs worked well around the functions parts. Do what you have to when it's cold! I was sitting a lot calling over a big clear cut, walked quite about as well. Scope functioned well this wayas I checked it a coupled times while I was out. Nothing is going to work well in the negatives. Ask locals and be as well equipped as you can. It worked for me. Best of luck to you.
Matt