As long as you can keep the wind off it the ambient temp doesn't make that big of a difference. I've cooked at 90F to -55F as long as I keep the wind off it or a heavy rain my UDS keep chugging along. My offset doesn't seem to care about ambient either but the rain effects it more. The BIG thing is colder air= more fuel being burned. So insulating will help with that. But I found it to be more of a pain then worth it. I used water heater wrap and some relfex bubble wrap looking stuff both caused more problems then worth IMHO.
Just my experience