Raybo, out here in the desert there is a type of cooler that is used extensively due to the low humidity called a swamp or evaporative cooler. It uses a simple float valve for filling the water reservoir that could be easily adapted as another option for automatic filling of the reservoir on your ET to the appropriate height without having to worry about filling every few days. If I ever get around to building some of these I will likely use one of those to keep them topped off. Any thoughts?
btw, here are a few example
images
Thanks,
- Aaron