I agree totally with Neil, you must read up in The Cornsnake Manual about hibernation and what you must do, but I have kept cornsnakes for two winters, this will be my third, and I have never done anything different from the other seasons of the year, except maybe reduce the length of time they have the light on in the vivs, to mimic the reduced sunlight hours.
I can also comment from experience that you do not have to hibernate the cornsnakes to breed them in the spring, as I have two cornsnakes sharing one viv and I woke up one morning to find 14 eggs layed, and the mum gently protecting them. This was about the beginning of July, and 10 of the eggs have hatched since, and now I have beautiful babies. I do not class myself as an expert cornsnake keeper, this event just happened because my snakes are happy and obviously virile!
I live in England, so the humidity isn't very good in my vivs, and the air dries out very quickly because of heating the house during the winter, but I try to keep a window open in their room to let a bit of cooler air circulating, which seems to help.