I used a cat litter pan. It's big enough to sit halfway on the UTH and halfway off. There's your cool and warm hide. My bp is also in a 20g long cage and the litter pan takes up about half of the cage. Water bowl is on the other side. Kitty litter pan is also flat when you turn it upside down so I threw some aspen shavings on top of that so that there is more crawling room if needed. Just an idea.