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I care for around 12 cats in our neighborhood. We feed them and allow them to sleep in our garden sheds and mudroom. Our region doesn’t get super cold – we only get snow maybe once or twice a year if that. It does rain a lot though. I put a large plastic bin with a hole cut in it in the mudroom with a blanket draped over it and a fleece blanket inside, thinking that should be warm enough, but a few days later when I checked the box I discovered the inside “walls” were wet from condensation. I realized I need to insulate as well. I will be following one of the tuts above even though cats have an indoor (but unheated) place to live. We’ve adopted several of the outdoor cats, but can’t adopt any more – unless they live outdoors. I want to start a spay and release program in my town.
I would recommend using some boards or a box that can also keep the cat's body heat from spreading away; i.e. build a little "leanto" in which you put the towels(spelling?).
OUTDOOR CAT ROOM — Gone are the litter-box odors and the food messes in our downstairs bathroom, forever. There's room for the litter-box, food, and water. It also features a galvanized mesh paw-cleaning mess-free floor, led lighting (swapped for a heat lamp when it's cold), and a place to lounge and view the woods. The cats have never had it so good! (Designed and built by Greg Piper 2016-03-04)Keep your cat's litter box clean. Cats in heat produce more urine, so maintaining a healthy litter box will help keep your cat from urinating outside the box due to sanitary reasons.My next problem was that after building the first one with a thickwall 'omaha steaks' cooler I already had, I couldn't find anyone selling large enough styrofoam coolers in november. So I picked up some 2" foam board at Home Depot which was a real win...foil on one side and waterproof plastic wrap on the other. 2x4' board was under $5 and I needed two. I cut one of them through the plastic waterproof layer and folded it into the bottom and two sides where the mylar/foil remained intact during the fold, then cut a front, back and top. I put it in the tub and found a cardboard box that just fit the inside, applied a few pieces of tape and it was perfect. No air transfer except for the door and much better insulation than the average 1" cooler. I might get away without a heat source here in northern california where <30 degree weather is unusual. Put the foil part on the inside as it'll retain heat. You can also buy some of those mylar 'space blankets' for about $4-5 or less and wrap those around the cooler for extra waterproofing/heat retention. Back when I had indoor cats I used to put a 2x3' piece of those into a pillowcase and my cats would lay on them as though they were cat magnets.OUTDOOR CAT ROOM — Gone are the litter-box odors and the food messes in our downstairs bathroom, forever. There's room for the litter-box, food, and water. It also features a galvanized mesh paw-cleaning mess-free floor, led lighting (swapped for a heat lamp when it's cold), and a place to lounge and view the woods. The cats have never had it so good! (Designed and built by Greg Piper 2016-03-04)All you need is a Styrofoam cooler, a box cutter, some straw, and a few boards to create this simple, effective feral cat shelter. Ask a local restaurant or medical office to donate a heavy-duty Styrofoam coolers—they usually end up in the trash, anyway. .This is a product created for owners of cats who want to provide the best level of comfort to their four-leged friends. This box enclosure has got a heavy bottom that increases stability. The product is made of wood, laminate wood, carpet, staples, nails and screws.