Wife can't be trained, at least I haven't been successful in the 7 years we have been camping together. She feels too much pressure in being back there and forgets all the previously agreed upon hand signals and starts failing around any time I get close to something. Even moving acceptably close like along the edge of the gravel on the drivers side of the driveway so I can maximize camping space will have her twirling like a windmill. She also doesn't seem to grasp the concept of if you can't seem me in the mirror, then I can't see you and I stop. Then she's confused on whats going on and throws her arms up.
Daughter has usually gone camping with us and she doesn't feel the stress and can stay focused without a panic attack so I've used her as my second set of eyes when available.
Luckily, I'm pretty proficient in backing after years with horse, boat and farm trailers of different lengths and hitch types along with dollies for aircraft containers as a former retired FedEx Express Ramp Operations Manager. Those things are about 8' long and just like a pivoting head hay wagon. That's the biggest challenge most of ever will face backing a trailer.
One of the reasons I got a backup camera now that our daughter is on her own and often isn't with us when we setup and comes later when she can. The wife takes the dogs on leash and walks them while I survey the space, make a mental note of anything I need to stay aware of and I use the get out and look method if it's tight and the camera isn't giving me the view I need to be sure.
Main tip I'll offer is survey the site intently. Walk it and stand in one of the rear corners if needed. I can't tell you how many times I avoided an issue by walking the site before I started my back in. Check limbs/overhanging items (Some folks forget to look up), items on the parking pad that shouldn't be there. Have found tent stakes in gravel pointing up where someone dropped them while loading up that could have caused a flat tire.
Good luck in working through to find a system that works for you. The main thing is take your time, don't get upset. Even with all the issues my wife and I have had trying to work through this, I never get upset with her. I just tell her "I got it, I'm good" and finish myself when I can see she's getting worked up. Camping isn't stressful unless we make it that way.