I've had a set of submersible LED on 2 "proper" wood mounts (along with the triangle reflectors) for about 3 years now - with (so far) no failures.
I also put a Jn box on the drawbar (again IPx6) with a couple of Bulgin "Buccaneer" skts - one 6 pin to feed the lighting board (on the A-frame with reverse & number plate lights) and a 2-pin to another Bulgin on the console to charge the boat battery en route to the slip.
Whole lot to the car via a 13 pin.
I got round the "failed LED" scenario by fitting std lights to the Short trailer board a bit like the "repeaters" you see on Lorries & busses up top. - that way if the LED fails, my "resistor" is an indicator bulb!
I posted the detail a while back - do a text search in this section for "manky plank"...