We now have two shelters: One we fabricated out of a Rubbermaid container and a styrofoam cooler, with a hole cut out for access. It sits on our front porch. Our adult male took to it right away. Most nights, you can see that he's burrowed inside. I've placed my hand inside after he's stepped out of it, and it gets quite warm. Granted, it's not overly cold out yet.
This past Friday, we picked up this
shelter from a local man who makes them. It has two entrances and an upper "deck" inside where the cats are supposed to sleep. We also picked up some straw and catnip (to attract them). We think the mother cat and her "teenage" son are already using it. We have it on our back deck in a spot that gets a lot of sun. I'm still thinking of what we can do to make it a bit warmer on the coldest of days, e.g., an electric pad or one of those warmers you can throw in the microwave. I sure hope they make it through the winter.