How to de-spook a horse?

I read both the other answers and even though feeding him in the trailer would make him want to get in, it teaches him the wrong lesson and if you have no feed with you will not work. Trailer training a horse is like training them for anything else, and is actually a lead training problem. you can have him trailer trained in a couple of weeks, but if the person pulling that trailer is not very good at pulling trailers they will scare him to the point he wants out at all cost. Sudden Takeoffs, sudden stops taking turns to fast swerving going down the road these things will scare them to the point they will eventually kick the doors off to get out. I have actually seen that happen. You must remember if you are riding in the trailer and the driving bothers you that it scares the horse really bad. I trailer train horses to load on command and un load on command.