Boat trailer lights.... wish I had a dollar for every one I've seen on the road with some sort of light problem. No exaggeration, but I reckon 90% I see on the road have something wrong with them haha.
Geoff, what type of lights have you got? If its the type where the wires connect to the lights with pressure and a few screws your going to continue to have problems with them. I have these and I drilled the back of the lights out, fed the wires through and soldered them direct to the globe holders. Then I silicone the holes up. They have no choice but to work now and had no issues for years.
Also, I think its a good idea to disconnect them before backing in the water as I've found the sudden cooling from the water prematurely blows globes and cracks the lenses. The stop 18W globe gets very hot, especially when you have had the brakes on for a while.