I have been using White Night backup lights from G.O.S. Racing. These attach to the trailer receiver and have worked great for just about 3 years.
One thing about a dually, is it's real hard to see behind you when it's dark. My driveway slopes sharply to the street for about 60 feet. I can see behind me and around the fenders really well.
Yes, the housing is plastic, but they throw good light IMHO.
I have some pics of them in my link below.