In cold weather, shelter is actually more important for stray & feral cats than food. Even though feral cats build thicker coats for Winter, they can quickly succumb to hypothermia, particularly in rain & snow when their fur gets wet and doesn't insulate as well. Also, stray & feral cats are more prone to parasites, respiratory infections and minor illnesses. Combined with cold, wet weather, these relatively minor maladies can quickly prove fatal.
Do NOT use blankets, towels, etc. inside the shelter!The inside will be exposed to moisture from outdoors and the cats themselves and fabric tend to mold and mildew.
Here is a pdf from the same site with ideas for building an outdoor shelter to protect them from the cold. These can be easily made with a plastic bin, a Styrofoam cooler, or with cardboard boxes for a temporary shelter.
I'm pretty sure this can work for dogs too, but you might want to do extra research just in case.
Always keep your animal friends safe, comfortable and happy!