My Kiev 4 is very reliable in snow and /or very cold weather. I usually just carry it around in a coat pocket and that seems to be adequate protection for it.
dI have never dared to take one of my Contax II s out when it gets that cold but the Kiev has never been a problem.
Anything with batteries is not a great idea. 20 or more below Fahrenheit is not very good for them unless you can keep them warm somehow. Around the fire in the lodge works great, outside...not so much.