I have a pair of conventional fog lights mounted on my fifth wheel that work very well for backing at night - and I have a couple of recommendations:
Mount them 3-5 feet from the end, underneath, aimed out and back at about a 45 degree angle (experiment with the angle). Aiming them directly back doesn't do much good because you really cant see straight back in your mirror anyway. You normally use objects to the side for a reference. Also put them on a switch instead of wired to come on when you are in reverse - you need them on all the time while you are positioning the trailer into a site. Keep it simple - you really don't need to have them switched from the truck. I mounted my switch underneath the trailer in the front. You are generally out looking around anyway. LEDs would work OK too if they are bright enough, but remember, you loose some light in your mirror. Make them brighter than you think you need.
I don't think any laws would apply because you can't turn them on while traveling anyway.