New here, sort of...I registered maybe a year ago, and with a very busy year, lost track. Now I'm back!
This is a very interesting thread for me, as I live in a rural area where there are LOT'S of feral cats. I often get asked what to do for them. As I live on a cattle/grain farm, there isn't much we have to do for them. They have straw and mice aplenty. But in areas around here, what some of my friends are doing, is constructing square straw bale homes, with a hollowed out centre and a small passageway, for the cats to emerge for food and water. It's important for this to be in a protected area as windchill values here can be dreadful.
In extreme cold, you need either free running water, or be willing to change water several times a day. For feral cats, water is first, shelter second and food last. Feral cats are pretty smart about food and shelter, but water is a tough thing for them when temps are freezing.
Where I live, if you don't have animals to house, Pole Barns are prevalent. These are (generally large) structures that mimic lean-to's in some regards. They will provide cover from snow for tractors and other big equipment that is not required in the winter. They are open in the sense that there are no doors, but they are sheltered from the prevailing wind and snow cover. My friend and neighbour (3 miles away - lol) has just such a structure. They have retired from farming, but still need equipment to keep up with the homestead lawns etc. She has a feral colony that thrives year after year. She has never seen the Mum cat, but the kittens get fairly friendly. When she can, she traps and neuters the kittens. The Mum is very cagey and has never been caught, the sly thing. In the end, there is quite the feline condominium happening in my friend's pole barn.
She feeds them, waters them and befriends the kittens so that most of them can be neutered and not add to the problem. I go there when they are on holiday to feed and water, and it is a fun adventure to see how the kittens react. Some are very gregarious and some not so much. It's always a treat to win them over.