One must be careful adding external lights to the rear of the trailer where you may interfere with the DOT RULES for required SAFETY LIGHTS.
In most states you are not allowed to add lights that are turned off when in travel mode mounted to the rear BUMPER or on the rear trailer wall. This may not pass safety inspection and in most cases have to be removed on the spot in order to pass.
Adding lights on the REAR OF THE TRAILER for backing into the camp sites for instance can be legally construed as BACK-UP LIGHTS but have to be DOT TYPE APPROVED and only come on when your Truck is in reverse etc... The lens have to show the DOT APPROVED number on them... These lights also are not allowed to be able to be turned on unless you are backing up and also cannot shine into the eyes of on-coming vehicles etc... Check with DOT... Back in the old days when running off-road jeeps etc we always needed extra lights and used to get away with putting socks over them when not off-road. That is pretty much not approved now anywhere.
Really behooves one to check the local DOT laws of your licensed state before dumping monies into external lights etc...
Adding lights for your own purposes may be allowed to be mounted on the sides of the trailer in most states but here again I would get a good idea from your local licenses state DOT office just to be sure what you can and cannot do. Would sure hate to have them removed on the next safety inspection.
Just saying...
Roy Ken