You're correct, JL does not offer HLCD, but RF does. I just mentioned JL because they're a high end provider of just normal near field range speakers that are one of the major players in boat audio. There's others that have HLCD's as well.. Bullitt, Krypt, Exile, WS, RF, etc are all the leaders in that market.

Are your speakers that you're using designed for marine environment? Do they have paper cones/woofers, styrafoam surrounds, etc? Or are they other materials that take wet moist weather better? Those are the kinds of things that bring these others' costs up. Not saying you couldn't compete, but I think you'll find there's lots of competition out there.