Sounds like mine and any other production boat I've seen, except I've never noticed rainwater in mine (it's mounted on a vertical part of the stern though, not a slope). They're poorly protected indeed, but then so is the other end (the one you plug into the marina outlet, at least here in Europe) - all just IPx4, which is splashproof only.
If you want something better, you can swap the end on your boat out for a Marinco socket (yellow, with black screw ring and screw-shut lid when socket is not in use). They're a bit better, but the plugs are not really waterproof (submersible) either - the socket with the lid screwed on may be (when nothing is plugged in). They also cost a silly amount (the only one I've seen around here was on an Oyster - where I've repaired it due to water having gotten into the plug). And that still won't change anything about the marina end.
I've just put some silicone grease on my socket pins to keep them from corroding together and so far it's fine.