It's probably not the best for it, but last year I kept my outback on its side outside the entire winter here in Alaska. One of the coldest winters we have had in a while. Weeks of 10 below zero weather with a few days of -20 tossed in. The kayak doesn't seem any worse for wear. I can't imagine anything on it that would be affected by cold weather. I was more worried about the UV exposure but fortunately we don't get much sunlight up here in the winter!
This year I have a bigger garage!!! Woohoo!!
I might be wrong, but UV is not effected by the clouds. Just like getting sunburned in cloudy weather....