Something a little more long lasting and effective for frosted combs and wattles is Castor Oil...can get it cheap at any pharmacy and even at Dollar General. It brings blood to the surface and can help prevent and also to restore a recently frosted comb. Need only put it on once or twice a winter if you live in constant subzero temps, take the rooster off the roost at night and apply it. It lasts much, much longer than Vaseline and works better.
Can't really speak of temps that stay that far below zero for that long but good ventilation in the coop helps, no matter the temps.