Subtrans is a sealed component. Make sure the breather line is clear of obstruction. Maybe even extend it to the roof line.
Note that if there's frost on the outside of your engine, there's frost on the inside; that's why it's so important to get them up to full operating temperatures - to burn off the condensation. The colder or more humid your environment, the more important this becomes. In really cold temps, you should be blocking off your radiator until the fan starts cycling normally. You'll have to experiment with how much blockage for your area and temps. eta: you don't need frost to have internal condensation.
