I added backup lights to my 5er several years ago. I didn't want them tied into the reverse lights because when you put the truck in D they go out and when moving forward you can't see how far to go before starting to back up.
I wired mine directly to the battery's using a switch and inline fuse in a compartment door on the passenger side. My wife gets out anyways to check clearances so she's the one that flips the reverse lights on. Plus I can switch them on anytime which helps when setting up camp in the dark. They only shine out about 10' past and about 5' out to the sides so they aren't lighting up the whole campground behind me.