The moral of the story is that this horse is NOT afraid, NOT angry, confused, or upset in any way. Ears comfortably forward, eyes soft, tail loose, blinking, trying to graze, etc. Getting on that trailer was JUST NOT HIS IDEA. The trick with him was to make it his idea. I led him as close as I could get him to the trailer, got him to look at it and stand quietly, but when he'd back away I would make that backing up my idea as well, if that makes sense (not "in his face" backing up, more like Showmanship type backing, calm, steady backwards movement). When he got harder to back, not as enthused about getting away, I immediately reapproached the trailer and allowed him to rest in it, no pushing back, no nagging forward, etc. Pretty soon, he got the idea that if he chose to go away, he was by extension choosing to work. Choosing to do as I asked and get on the trailer got him rest and relaxation.
I don't see that there is much physical force involved here. This particular horse has been proved to that he is stronger than a human, and if you try to force him physically (i.e., drag/shove his butt on that trailer) he WILL and HAS thrown his weight around, which I cannot hold, so I can't afford to start something I can't finish. All firm, gentle request, no pushing, no pulling, no food motivation, happy horse, happy owners. The funny thing is that many owners take it personally and think that it's because they were ten minutes late feeding this morning, or they were out of town and a neighbor did the last barn check before bed. IMHO, horses don't have an "I'll get them back" capacity, or a spite gland.
So, there's my novel for the day, lol.