i have the same problem and i worry about my ball again this winter. we had a heck of a time maintaining proper temps last winter. so... i took a UTH and added it to the inside of the lid of dexter's enclosure. and i'm going to monitor his temps as the days and nights get cooler. i also moved him into my bedroom... cause it's warmer in there (i keep my tarantulas in there as well) so hopefully the temps will be fine.

if not... i'll add a heater to the room.