backup camera is the way to go. I always hitch up my trailer solo while my wife is corralling the kiddo getting food packed. Before the camera I used to look over my right shoulder and imagine a straight line to the bow of the boat which usually got me centered. I would then get close enough while still knowing I wouldnt hit the trailer against my truck, hop out and get a more accurate distance and just inch my way back.
But with the camera, it takes maybe 5 minutes to back up, hitch up, pull forward, throw on my swim deck and pull out of the garage.