dog house that she found for next to nothing at a flea market. It was a 2 piece unit that had a a bottom piece (with bottom and sides) and a top piece that was the roof. She glued mylar on the inside using spray adhesive. Then she used a styrofoam cooler (with a door cut out) on the inside and stuffed straw in the spaces in between the dog house and the cooler. She said it needed to be wheat straw instead of hay, because hay gets moldy. She put blankets in the cooler and made some kind of door/curtain out of an old wool blanket to keep out the wind. I think she set it up on a wooden pallet to keep out the damp.
I also have another friend who has a feral cat who lives in her back yard. She made a very snug home for her using a small dog house with a flap door. She put an (outside) heating pad underneath it and the cat hardly ever comes out except to pee and eat.
Another friend made a feral cat home using a cast off dog igloo and just stuffed it with straw. It was pretty cozy for the mild winters we have in the south.