Thelma and Louise Sleep Inside

We're looking at a really cold winter, so I spoke to my Glugster and we decided that we would start training the girls to sleep inside the house overnight.
The girls sleep outside in their igloo, and because my cats are indoor cats the doors stay closed so they can't get outside.
Bringing the girls inside meant they had to be taught to sleep only in one place, and they had to be taught that the cats were off limits. With Thelma and Louise already having responded exceptionally well to simple training like sit, stay, I was sure I wouldn't battle.
So we brought their cushions in off the outside couch, and blankets, and I started training them.
It is fabulous! The girls already know they are not allowed in the house, so I had to teach them they could come inside if I invite them. They come in when called and they go straight to their cushions in the corner of the dining room. I've let them know that that room is their space when they're inside and even if I barricade the room and remove the barricade in the morning, they don't come out of the dining room until I call them to the back door to let them out again.
I am so impressed with how well behaved the girls are! I put down newspaper and if they need to mess in the night they do it there.
We have had a couple of barks in the night, at the cats who want to go and see why the dogs are now sharing their space, but apart from that its all good.