I do it all the time. Mostly I just get out and look until I'm sure I'm not going to blatantly hit something. I find I can still see my wife from the light of the taillights.
If you have a truck you can hang a towel or something over the truck taillights so they don't reflect off the front of the trailer and back into your eyes.
Some people lay out some rope light on each side or at least one side of the spot. Then they can just skirt the lights with a tire.
If you bring a shop light, make sure it's not at the front of the site but rather further back into the site. It might even work to point it at the ground and just navigate by the light reflected off the ground.
If you decide to wire in some permanent backup lights, mount them on the sides pointed back at the tires. If you mount them on the rear bumper the trailer will block your view.