How often will you switch it off? Can you just use a breaker?
For the power to my pier, I have a series of breakers. The first breaker is in my main panel in our house, a 30A double pole breaker. Wiring runs from there under the house, then underground to the top of the stairs to my pier, about 200' away. There, the wiring goes into a weather resistant main lug panel with a 30A double pole GFCI breaker -- so everything downstream of that is GFCI protected. Wiring then runs down the stairs another 50' or so, into another weather resistant panel on the pier. That contains a 15A single pole breaker for a receptacle, and a 20A double pole breaker for my boat lift.
When I stop using the pier in early winter, I will shut off the 30A breaker up inside our home. Or if we will be out of town for more than a few days I will shut it off.
For routine use during the boating season, I switch off the 15A and 20A breakers on the pier when power is not needed. I don't want power going to the boat lift control unit unless I am down there actually needing to use the lift.