Review on SAE Power Socket Sidewall Port 2 Pack with 8 Screws, SAE Plug, Weatherproof Quick Connect Solar Panel Mount, Universal Flush-Mountable Connector, 12AWG Cable for Solar Generator Battery Charger by Eric Krull

Be sure to install it on a vertical surface if you need water resistance. The flange is somewhere between plastic and rubber, making it suitable for surfaces that aren't perfectly flat. Generally good devices and worth the money. 2 of these installed for our solar powered sailboats. Use a 7/8 bit to make the main hole for it.