You're probably going to need some other heat source, for two reasons: One, the heat mats you have are pretty low wattage (they have to be, otherwise the floor would get too hot) and probably don't produce enough heat, period, for a colder room. And the second is that the bottom of the AP cage is thicker than your plastic tub and will not let as much heat through from the heat mats. Either a CHE or an RHP will do the job. Of the two, the RHP is probably easier and more efficient since it doesn't get hot enough to burn from momentary contact, and it mounts inside the cage. With the CHE you'd have to either cut a hole and cover it with screen and put the CHE fixture above the cage, or put the CHE inside the cage with a safety cage around it. The t8 doesn't have all that much head room, so putting a fixture inside that sticks down that far is probably not ideal. Putting the fixture above the cage means you'll lose more heat to the room, and you don't have the option of putting anything on top of or above the cage.