Here are some ideas about keeping ferals safe in the Winter, based on my experience, and my human's experience with the ferals both before and after I was around.
The winter I was alive, we lived in a shed. We eventually had lights in the shed, but I don't remember if that was before the end of my winter or not. With electricity, we can have light bulbs (or heatballs, as come call them ), and an electric heated water dish. Remember to keep the water dish full, or cats will sit in it
However, you also have to keep the kitty litter from freezing. The ground outside is frozen, so it is harder for us to cover our messes. If the litter gets frozen, we might not like to use it. In fact, that happened during our winter.
We had some cold days before we had a heated water dish. So what he had to do was bring hot water (he just let the hot water run from the tap) out to us so it lasted a little longer before it froze. Often, he would feed us, then work on getting the ice out of our water dishes, then pour the water in the dishes. Sometimes, the dish cracked a little, too, so it could only be used for dry kibble later. When we had some water after we ate, he was sure to call us Good Kitty. He knows that kitties have to have water to survive. Sometimes we could drink snow, but we might not have thought of that, and there were some cold days without snow.
We had some blankets out there, but often we kept warm by sleeping in a big pile of lots of kitties in the shed. Sometimes we would get up in the night and go do something, but then we would usually comme back. We had boxes, too, and some of them had blankets.
The current setup for Smudge and the rest of the kitties involves square hay bales. They say straw would keep us warmer than hay. Well, for one thing, they don't take the straw away to feed the cattle, as they sometimes do with the hay bales. But we have been able to make our little hidey-holes between the bales to keep warm. In our currrent setup, we get sun and are protected from the north wind and the west wind. There has been some talk of building a dedicated cat house separate from the barn.