The two closest drive-to campgrounds to the mouth of the Moon R. are Horseshoe Lake (privately owned) and Oastler Lake (Provincial Park).
Moon River Marina on Woods Bay should be able to rent you a boat. Keep in mind, once out of Woods Bay, this part of G Bay is infested with prop eating shoals...so a lot of marinas have got out of the rental business.
Gordon Bay Marine on Lake Joseph also rents boats...if you want to cruise past the shacks of the rich and famous...