Many modern monohulls are now equipped with fiber optic lights. This should be really easy to adapt to trailer lights. The light sources are simply located inside a little box up by the tongue of the trailer and fiber optic lines run to the desired locations. It's really easy to make one little light box waterproof. All the rest of the components in the system are non-corroding plastic. I woudn't be suprised if someone already makes a kit, but it would be an easy DIY project if not. The light sources could be LED's if you desired.

Jimbo