I use a different model that they have on the same website that transmits on 433 Mhz which connects into a weatherstation ($60) that I have. What I did was attach the transmitter to a piling and made a little roof over it with flashing. I inserted the sensor in a 1/2" PVC tube and attached it under the dock. If it lasts two years then I would be happy because it sure beats going outside and dipping a thermometer.
Also by inserting the sensor in the pvc tube I was able to place it at a specific depth, always 2 feet beneath the surface. It's a floating dock.