The longer the trailer, the slower it is to react to driver input.
Have a spotter to guide you, figure out the communication lingo between you 2 before you start, and just do it. Its easier than you think. But you have to have a spotter if you will be backing in from the passenger side. If you could do it from drivers side then you could get enough adjustment out of your mirror.
Maybe put some kind of markers on the gravel, such as spray paint, exactly where you want the trailer so your spotter knows the exact location.
