Backing up to load the camper is easier, I find, if I turn my head and right shoulder around to watch the gap between the camper and truck close in and not just look in the rear view mirror. Light on the clutch or brake until the truck juuuust touches. Then set the emergency brake, shut down the engine and inspect that the camper is flush with the truck at the cab. Plug in the camper umbilical to the truck and lower as soon as possible to reduce any strain on the jacks if the truck is pressing into the camper too much. I'm rarely off more than an inch on one side or the other on the first attempt. If I am, I pull away from the camper, turning the wheel in the same direction as the gap. If the gap is on the right, I turn the wheel to the right and pull forward a foot or so. I then straighten the wheel and back up that foot and check again. Repeat as necessary.
Another trick is to mark your tire tracks as you pull out from under the lifted camper. Upon return, use those marks and roll the truck back over them. On dirt, it's easy as long as you preserve your tire tracks. On other surfaces, a can of spray paint, the type the highway department uses or the type used on sports fields since they wash away with the first rain can mark the tire tread path.