Well, we had a similar situation, a horse we got was tied in a trailer by the previous owners, and he was in the back stall of a slant... He tried to back out, and they just opened the butt bar and let him, even though he was tied. His back feet slipped under the trailer and his head was tied...... They just left him until the halter broke. *******S.
But anyway, he REFUSED to load in our horse trailer. He loaded fine in a stock. So I started just putting grain in the front of the horse trailer, and just letting him eat in there. At first he wouldn't even relax enough to eat it, but after a few weeks he would take some nervous bites. He would try to run out as soon as I let him turn around (it's a 5 horse slant) and so he just ate it facing forward. Then I would let him turn around and make him WALK out. Months and months later, he's our best horse to trailer, LOL. My dad took him out about 7 weeks after we got him, when he was still nervous about the trailer..... he just loaded him up, closed the divider, and took off. He was probably scared silly at first, but after he realized he was okay, he just.... was fine. His only problem now is that you can't tie him. That's okay though, you don't really need to tie in a trailer with dividers. Maybe try just... taking him for a ride, showing him that it'll be okay. Maybe you could just have your hubby drive a few circles while you're in the second stall, IF you think you're safe in there, and that way you can soothe him. Or, if you're not really safe, maybe just a short, easy ride in a trailer would help him see. I don't know though, every horse is different and I don't know what his accident was. But if you think he could handle it and it might help, it's worth a try. I don't know your horse, though, too. If you think that won't help, don't. Just what helped in my experience. =) GOOD LUCK!
To rein a horse is not only to guide him,
but also to control his every movement.