Cujo1 wrote: mount your lights on your side bunks away from the boat and they won't get destroyed each season in the ice, etc.
The lights on my main boat trailer are up on guidons, 4 feet above the ground and protected from the boat by 1x2 steel posts. I still have to replace them about every 3 years. They get damaged...by something; rocks flung up by the truck (even though I have Lexan shields on them), ice, garage doors, fenceposts, boat, unknowns, etc.... no matter where they're located.
You are right, though, the higher you mount them, the less susceptible they are.
The tip about the grease is a good one; it will prolong the life of the sockets and bulbs by about a year.