I had to laugh! Not quite the use I had expected!! Kato looks a bit disgruntled, and Ava on the otherhand was squished out like a sausage and loving every minute. I couldnt quite work out why she was so happy until I put my hand down the side of the tent. It was TOASTY. The cardboard turns out to be pretty insulating, especially combined with the warmie (and 2 cats).
They do actually use the tent together - as a tent! When I come back home to a freezing house, I will usually find them curled up together inside the tent; the warmie is set every morning (just 4 mins in the microwave).
Of course, at night time they use human body heat. And it works both ways. Sometimes I even have to stick my feet out, they keep me so warm!!
And on the odd occasion when we havent set up a special warm spot for them, I have come home to their own creative solutions. I have never seen Kato in action, but he appears to know how to roll himself up in something, as well as burrow through an opening.