This shelter requires you to invest in a marine cooler, but it really pays off in the labor it saves you. Similar to the Super-Simple Winter Shelter, all you need to do is cut an entry hole and add a couple of finishing touches. The skill and tool level for cutting the hole is slightly higher than the Super-Simple Winter Shelter but still well within the reach of a beginner. Marine coolers are available online at a deep discount with free shipping in the off-season, which happens to coincide with cat-shelter season. They come in large sizes — a 150-quart cooler can sleep 4–5 cats. The cooler is insulated and water-tight with a locking lid so there is no need to caulk the lid, and it is heavy enough that it doesn’t need extra weight added. The inside is smooth, hard plastic that cats can’t scratch up. The hinged lid makes it easy to check on the straw during the winter and to clean the shelter.
Measure, mark, and cut a 5½” diameter hole in the box a few inches from the top and off to one side. The cooler is composed of an inner and outer layer of thin plastic with a thick layer of foam insulation in between, so you need to use a box cutter or other sturdy, sharp tool to cut the plastic and then use a longer blade to cut through the foam. Tape over the edges of the hole to prevent leakage, add straw, and you’re done.