Hey! Speaking from experience- skip the rubber made houses. The cats are too scared to go into it bc once they’re in there- super easy to be ambushed by predator. So what does work? Get one (or two) heating pads (brand sunbeam is my favorite) extra large. Take off the cloth and plug them up outside turn them on high. We’ve tried everything over the years, this is the best answer! The cats are obsessed with it.