I have cooked in my UDS below zero as well. Keep it out of the wind, and prepare to use a little more fuel with intakes more open than usual. Search the forum, I have seen posts from a guy in Alaska cooking on his UDS on temps as cold or colder than Harbor.
I agree it's a draw. Metal thickness is close to the same with a very similar setup inside.
KCBS Certified Judge
Weber 18" circa 1965
2 22" Weber Silvers and 1 22" Weber Gold
King Pig UDS
Tejas Charcoal 2452 Grill, 28" discada
Char Griller King Kamado
1 Smokey Joe and 1 Mini WSM
Currently building a 22' Portable Kitchen www.bullybbq.com