I have the same trailer and am getting more confident! The marker or cone on the ground where you want the trailer wheels to end up is useful. Another suggestion that came off a forum is this - Say you are backing in with the end of the trailer turning toward the driver side (the "easy" way).
You will have your hand on the bottom of the wheel and will be moving your hand left towards the driver's window because you want the back of the trailer to turn left towards the driver side. The trick I learned is BEFORE you start moving, turn the wheel as above about 1 and a half turns to pre-load it, so to speak. Then start slowly backing. Seems to work well and make the corrections easier. After a while you won't have to stop and think which way to turn the wheel. The mirrors can be confusing at first, so it sometimes helps to roll down the window and look back until you are more comfortable backing. Also, don't forget about the front end of the truck! Sometimes that is more the problem with posts and other vehicles. Remember, if you go slow and don't get rattled, you're golden! I actually prefer to do it myself without others waving their arms about and giving conflicting directions about which way to turn the wheel.
Even if you get out multiple time to look at how things are going, that is fine. If this old lady can do it, anyone can.
I do so love it when I have an audience and nail it on the first try.
Tina & Ted & pooches
2012 Ford F-150 XLT 5.0L V8 4x4 with tow package
Andersen WD hitch with sway prevention
2012 Rockwood UltraLite 2304s trailer