Well it is certainly worth a try...I am in West Texas and our winter/coldest months tend to be Feb-March. What sort and size of plastic balls? How deep is the tub of water?ok this may sound crazy. but i use tubs for waterers and float 2 little plastic balls in them. if wind or anything moves the air the balls move and keep the water disturbed so it doesn't freeze. living in East Texas our really bad weather does not come till late January.
Lots of people do use water heaters. Some use the models that are for keeping bird baths from freezing. Others fabricate their own solutions from light bulbs. Then again there are actually units designed for poultry waterers.definitely cool ideas ... so no one recommends those water heaters then?