I overwintered 3 carniolan single deep hives last winter, and all did fine. Although, I put 3 inch thick insulation on top (with plastic wrapped around sides)- insulation makes a world of difference in how much honey the bees eat. It makes it much easier for the bees to move around and get to stores also. In fact, there was a 30 degree difference under the insulation vs. outside... in other words, insulation makes it feel 30 degrees warmer for the bees.