If you keep your pre-lubed patches in an inside, shirt pocket, your body heat will keep the lube softer. I do recommend changing the lube when it gets much below freezing, by mixing either more oil or alcohol with your usual lube. I have used alcohol for a " lube " when shooting at the range, instead of a spit patch. I think a thin vegetable oil with some alcohol in it, or even one of the window cleaners with alcohol will also make an adequate patch lube, at hard freezing temperatures.
When you get out in -20 degrees, and lower temps, then I think you have to consider synthetic oils made for aircraft industry use. Ballistol( mineral oil with additives to remove mercury), and olive oil also seem to work well even at these obscenely low temperatures. Jojoba oil is also another oil that seems to stay liquid at low temperatures.
The air is so dry when its below freezing outside, that Black Powder generally remains very dry in the barrel. Don't be taking a loaded barrel into a warm car, truck, or home, however, as the warmer air will hold moisture which will condense on the colder barrel. If it gets inside the bore, it will foul the powder.
One of the advantages of using a Horn to carry powder in the field, instead of a metal flask, or metal container is that horn quickly assumes the temperature of the atmosphere around it, and moisture doesn't condense on it surface, as it will on any metallic surface. Plastic containers are as bad as metal one, for condensation, so they also should not be used.
When hunting out in snow and cold, I tend to keep my powder horn, and my lubed patches Under my coat in my hunting pouch. That allows the heat from my body to keep these objects warm. I wear several layers of garments against my skin so moisture is trapped in those layers, and is not condensing on the powder horn or any of the items in my hunting pouch.
