Well, that's because I don't feel that the problem lies in the trailering, but in the other horses. Does that make sence?
That's what I said made sense & didn't want to sound lecture-y about.
Ace is a type of equine sedative... & it sounded like you could do with a few tots of 'Dutch courage' on the day yourself!
I missed the bit where you said this was all going down in a year & a half. Therefore I'd personally be concentrating more on preparing him and less on researching sedatives for now. Whether or not the prob lies in trailering, if you're going to put him in one & he's had little experience with it, I think it's still very worthwhile to do some training there. While I don't do stud chains & the likes, if you're not sure of your ability to control him, teaching him to yield & respond to you on a long line is also a good move. As for other horses, is he generally a problem in that regard, or has he had little socialisation with them or such? I don't know your situation or how hard or impossible it may be for you, but bringing other horses, or taking him to others for visits with sociable horses one on one, will give you a better idea & help prepare you & him for what may go on at the new place.