I ended up moving to a 50 watt submersible aquarium heater. I went with the Aqueon (pic below) one – primarily because it had a built-in temperature control. This will allow me to either max the heat out or adjust it if I needed to.
I tested it in a 1 gallon container as well as my 5 gallon carboy. The heater worked well and will heat the water in both congtainers, to about the same temperature +/- 1 degree. If you consider the difference in volume of water, the greater you go, the more heat distribution you should have, so a larger container should provide more efficiency and a steadier temp – I just didn’t have the room to keep a 5 gallon carboy in there, when it could be filled with wort.