I have been doing some experimenting with this heat controller. It seems to work good so far. You can set the temp you want, and how many degrees that the water can cool before turning itself back on. I'm sure it is much like the temp controller in commercial tanks. Nice thing about this one is that if you need 5 gallons of water heated, or even a larger amount, it's quick and easy to use.
This particular controller is rated at 1200 watts. I have been using a 1000 watt heating element with it as you can see in the photos. This would work great for a dipper that doesn't have a full size tank and needs to heat smaller amounts of water.
I bought the controller and heater on Amazon, but I'm sure they are available elsewhere. Price was reasonable.
I have used the bucket heaters for many years when I was in construction. Wish I would have had the controller back then.