It depends on how often you get belowAnd are you saying I should have a backup heat source for those -30 days? Do you know if those "cozy coop" or other wall mounted infrared heaters work well enough?
-30C, and how long it stays that cold. A few short dips would be fine.... but if it stays in that range, or much colder for weeks at a time, yes I would consider some kind of heating option.