You can sometimes buy solid surface (Corian, Swanstone, Pionite, etc) in widths 18" or less. You can't buy wider unless you are a certified fabricator. You CAN buy Ecotop, Paperstone, or a few other niche solid surface materials. I work with those all the time. Be aware that ANY solid surface material is going to be heavy and miserable to work with. Corian and similar thin materials need built-up edges or
strict observance to cutout radius and setbacks, or cracks will propagate.
If using plastic laminate where moisture may be an issue, like on a sailboat, it is considered good form to laminate both faces of the substrate.
Industrial particle board is the usual substrate; not sure how good that is on a boat. At the very least, I would advise varnishing or painting the underside of the particle board. I always do that near sinks or dishwashers.
Finally, consider Dog's suggestion of Starboard -- aka HDPE or UHMW (polyethylene). It's the familiar cutting board material, and it can be used directly as
a cutting board. (Still want a separate cutting board for meats, and possibly another for garlic/onions.) It's not fabulous to look at, but it has a lot going for it:
-- Easy to cut, shape, and install.
-- VERY hard to damage. Doesn't split, crack, or chip.
-- Inexpensive and available in small or large pieces.
-- Dead waterproof. Reasonable weight.
Downsides: not all that heat resistant. Boring white. Can't really be glued, and you need to be smart with your fasteners. Cheers!