gdgdad, if you have Dollar Stores close by stop in and buy a couple of these sun shields for cars.
When you open the package open them up fold them in half the (the long way) make a crease then cut them along the crease so end up having 2 long pieces. Each piece will fit perfectly wrapped around the 5 gallon buckets starting about 3 inches below the top lip it will cover a little more than 3/4 of the buckets preventing the inside from getting steaming hot from direct sun.