A friend of mine had one hive in a bear-proof chain-link cage. I put four of mine in there, too. I was in the neighborhood yesterday and stopped by to take a look at them. All the covers were off and they were all dead and filled with snow.
Turns out he thought he had a good idea for wintering. He had pushed them all together, put a whole sheet of polystyrene insulation across all of them, and put rocks on top of that.
A strong wind got under the polystyrene sheet and blew it off, and all the covers as well, because they were frozen to it.