I find the rear window nearly useless for backing a trailer. You are looking through 4 layers of glass forming a tunnel view. I've backed the trailer using the side mirrors, but if the trailer is narrow, you will follow a somewhat winding path as you see it peek out one side or the other. A rear view camera helps a great deal, almost like a center rear view mirror.
By far the best is a front hitch. I finally put one of for a different reason (motorcycle carry) but have since used it to maneuver trailers around the yard - it makes things ridiculously easy.
