I have an exposed charger on my Jon Boat.

I got a 3 wire to 2 wire connector plug. I cut the 2 wire end off and put silicone seal where I cut the plug pins. When I am not charging the batts, I plug the ac cord into the plug adapter. Keeps plug from getting damaged. I also put a small amount of dielectric grease on the ac cord connector pins to keep it from corroding.

Cheap fix and works well.