I agree with the previous authers. Also, orient the winch on the pad such that the water will drain out of the inside. This may not make sence until you look at the inside of the winch pressed up against the winch pad. This is essential. Perhaps ask a rigger or winch salesperson to explain further.
Also, my preference over regular silicone is boat life''s "life seal" This product also contains poly sulfide rubber, and I think is far superior to silicon.