I would recommend an oil filled heater on a ranco t-stat. Thats what I use in the winter and it works great. They also make 400 watt oil filled heaters that are much smaller if you have a smaller area. i use the small one in my breeding room or when I only need to bump up temps a few degrees like in the summer just in case or in my breeding room which is kept cooler. Here is a pic of the oil filled around some of my racks, the Ranco t-stat is on top of the freedom breeder rack.


You can't see it in the pic but there is a ceiling fan in the room to circulate ait to keep temps even.