I had my bp in a 15qt tub in a rack made from 1/2" pvc. In a room that was 68-70F, I had to put heat tape under the entire tub. I had one section to keep the cool side in the high 70's/low 80's and another section of heat tap to keep the warm side close to 90F. I also found that I needed a space heater about a foot away from the rack. It was in the corner of a large room in a very old house, which probably didn't help much.

Like the others have said, if you keep the tub in a smaller room, your chances for keeping it warmer are easier.