Yeah, I can see a cat liking a fort setup. I'd worry about using a heater with mine because the girl that howls also likes to chew on inappropriate things. She might try to chew the cord.

They've been so quiet today that I just went to see what was going on. The younger, less vocal one was sitting next to her bed. The howler was curled up in her bed, completely knocked out. I had to check and make sure she was breathing!