This is the same setup I've used for years to bottle condition in my cold (~50F) basement. I also added a small submersible pump from Harbor Freight to keep temps uniform. Works great. Add a splash of bleach to the water to keep it from getting nasty.
Also: the cheap aquarium heater thermostats fail all the time. I eventually upgraded to a really nice heater that is fully plastic enclosed (much more durable). It was more reliable, but still failed eventually. You'll be fine, just check temps frequently.