Winter enclosure

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So I have a larger redfoot that needs to be inside for the winter. Last year I kept her in a bathtub with a heat lamp. This is not ideal to me as I am paranoid about a fire happening and she seems to want more stimulation than 4 white walls. She likes being in a plastic tub in the kitchen as it gives her plenty to look at and there are always people or other pets around. Also she can get some sunlight where that is limited by the small window in the bathroomI have a large one for an xmas tree but the issue is heat. We cannot use heat lamps as the cats would end up knocking them over. I have considered using a heat pad attached to the side of the tank but most are not rated for plastic.

I know heat from below is not considered the best option but what about setting the tub inside of another of the same tub so there is a slight airgap at the bottom and placing a heat blanket inside of a third of it? Plenty of room for her to get away from the heat but enough to raise the ambient temp to a comfortable level. And something the cats cannot get to.