If it's any help, I'll explain my method of backing up my trailer solo...
First off...everything I do, I do it in TINY increments.
Before I back anything up, I walk around looking for anything that may jump out at me...like overhanging branches, picnic tables, sleeping dogs...whatever. I plan my route of travel backing in, just as much as my route of travel getting to the campground, I just don't plan on any rest stops along the way.
I'll get the trailer oriented in the general direction of where I want it to go, but before I commit, I stop and get out and do another walk around...who knows, someone may have moved that picnic table on me.
I should now be 6-10' out from where I want to park the trailer. This is when I start using my SECRET METHOD of backing up...
I back up with my drivers door open and watch the ground to gauge my exact distance of travel.
Example: If I have the trailer set so I only have to back straight-in, and only by 8 ft, I'll make a mark, or pick a feature 8' behind my drivers door along the line my truck and trailer is going to travel.
Note: Don't use as a marker, anything that a pet might like to eat or play with...trust me, that comes from personal
Slowly... slowly... back up... slowly... slowly... scan your mirrors too... naturally watch and make sure that the trailer isn't deciding to not co-operate, or that the picnic table hasn't moved on you. Going slow keeps you from screwing up the direction your front wheels must be. Inches of travel at a time... there's no need to hurry... especially pay no attention that every eye in the campground is focused on you and your back-up prowess.
Watch for the bottle cap, rock, or cigarette butt on the ground you picked out as your 8' marker. When it's is now right under your door hinge you've traveled exactly 8'. Stop, put the truck in neutral or park, put the parking brake on, get out, and do your last check.
See? That wasn't so bad was it?
This is just a variation of a golfing trick for putting...picking out a landmark 2' from your ball that is on the path to the hole. Lining up your stroke to hit that mark is a lot easier than aiming for the hole itself.
This method works especially great for me to get my truck backed up to my trailer hitch. I'll put that hitch ball closer than 1" if I stop often, and get out and recheck my progress as I back up. By watching the ground right below my door, I can easily gauge distances a lot better than watching mirrors.
Besides, my dog is my only companion, and I can't get him to guide me back at all.
The true secret is TIME...take it slow, there's no rush...take time to think things out...make it a Zen-like experience.