Well what's some one from the deep south writing this?
For most of my cooking life I've used a charcoal/wood barrel cooker & in the winter at hunt camp you either cookd on it or ate Vienna Sausage
What affects the loss of heat ? Main ones are
1) Surface area of heated area.
2) temperature difference between cooker & air.
3) wind constantly brings cold air in contact with cooker not allowing the surrounding air to heat up.
4) Rain or snow brings water which is a much more efficient conductor of heat & brings evaporative loss into play.
How do you modify these factors?
1) in an offset build the fire in the main chamber, it markedly decreases the heated surface area. The main chamber of most offsets works great as an indirect barrel cooker.
2) If windy a simple wind block will help greatly, as simple as a couple blankets hung ( make sure far enough away & can't blow into cooker)
3) insulation for your cooker. I have an old welders blanket, it's cheep I wouldn't use for welding but works great for a cooker.
If it's raining or snowing either get cooker under a cover or eat Beanie Weenie