I got my babies a 1000 gal storage tank and made it into a house for them. I put a whole bag of shavings in it for bedding. They seemed curious about it and even went up the ramp to investigate it. But they won't go in it. I helped billy up into it and he stood there for a second and then jumped out of it and ran. Is there anything I can do to get them to use it? Should they go in it if it gets cold enough?