Bank of Dad- I have an off side rental spot, I also drive over the road (semi's).
Same size trailer as yours, what works for me is pulling past the slot, and slow and sure steer left not allot, just enough to get it to wander to the hole or slot, then remember,,Small slow adjustments and always come back and follow it in.
I do this with out a spotter most of the time in late evening (before closing time).
I rarely try to "One shot it" Meaning get it done in one backing. I am no way a "Hot Dog".
Once I get it going into the hole I will stop and G.O.A.L--Get Out And Look!
I have to put it between a Conex box to the right and a recreational trailer loaded with quads and gear to the left.
There is enough to pull up and straighten it out once I get it in half way.
I have placed a 2x4 on the ground as a depth gauge and will slowly back it in until it bumps the 2x4.
Remember if you make an adjustment (turn the wheel) as soon as it (trailer)starts to move in the direction you want,,slowly, start to follow it back.
The most common mistake made is watching for to long as it starts to turn. By then it will turn to far before the truck corrects as you turn in the opposite direction to correct, hence truck and trailer look like a "Snake with a sore belly"!!
ALWAYS G.O.A.L!!
