I've used mine all the way down to 10* in the snow and it does just fine. you will need to have the air vents open more than you would in the summer months. it won't burn as long in the colder months as it would in the summer due to the heat loss. most guy's just put a welding blanket over it and it works just fine.
I don't have direct UDS experience but I have BBQ'd down to zero a lot here in Nebraska. The packing blanket is a must on a single wall design partly because it reduces heat loss but I believe mostly because it prevents the wind from stripping heat off the same piece of steel you're trying to cook with. Since your draft has to be left exposed I designed an intake cover that seamed to really work for windy days. After the UDS is built and working, try putting a 90 degree intake (ductwork) over the draft that comes out and straight down. Just build it out of scrap tin, sealed against the side of the UDS - maybe attached with magnets. Buy a couple pieces of the extra course scotch-brite pads and cut them with scissors to make a plug and lay a single layer (1/2 inch thick?) of this over the intake. I've experiment with this and you'll be able to keep a birthday candle lit in your firebox in a hurricane. Now your fuel consumption/temp stability/recipe etc all start to work like they did back in July... Hope that helps...
And on the eighth day God created barbecue …. because he DOES love us and he wants us to be happy.
Current smokers: Egor (trailered RF) and Easybake (tabletop pellet drive)
I think I'm gonna build one anyway, and if i have problems, I will try a water heater wrap. I really want to build a revers flow smoker, but I haven't found the right material. The UDS will be a fun build, and when I do get the stuff for the offset one, Ill probably donate the UDS to one of my Friends, they love my BBQ
If you have any large friends that work outdoors like I do. Then just ask one of them to donate one of there old blanket lined carhart coats.
Thats what I did. LOL and it works well. He had a 4x blanket lined coat that had seen better days. Stick that coat on her and button it up. Kinda sucks to have to take it off and put it back on but it sure helps with temps.