I used Vaseline, and their combs did not get worse...did not fall off. From that point on made keeping the coop dry a higher priority than providing warm food or water. Kerosene heater helps warm the general area with dry heat.
We live in central Wisconsin. Our shed/coop has no power, so below zero nights are a challenge. Although they could probably survive it, we use a kerosene heater on the coldest of nights. Works pretty well, and it would shut down if it got knocked out by any pesty critter that might be running...