This is how I mounted my ballasts. Like OE does, but maybe not as pretty looking... Anyways, ballast is snug into container, container is snug underneath bumper. Some water may hit container, very little will enter container. The big hole in one end is stuffed with a home made rubber flap (not in the picture). This one is not air tight either. The intention with is to divert high water pressure, not submersible proof.