Cold coops and Eggs

I have seen a lot of information on here regarding keeping coops in the winter time and not using a heat source, also keeping proper ventilation to keep the coop as dry as possible, but I am wondering if any of you have a problem with your eggs freezing in these conditions?

I live in Northern Wisconsin so it gets cold, below freezing almost every day from Dec-mid March/April and it can get well below zero in Januaray-March. I would like to build roll away nest boxes to keep eggs as clean as possible but if I have them roll to the outside they will definitely freeze, and I worry that if I don't heat the inside with a lamp in winter that the eggs will even freeze inside, of course a big enough flock in a proper sized coop should aleviate this concern.

Anyone experience this?