If you travel alone you might try taking the partition out or fastening the end of it over to the side. This gives the horse an opportunity to spread his legs out so that he can brace himself, especially on turns. Even if you are trailering with two horses, as long as they are compatible, you might be better off without the partition. Given a free choice, horses will usually stand kitty-cornered, perhaps because it allows them a little more room. They also enjoy being able to see out, just as you do.
Many horses travel better in a stock trailer than in the confines of a two horse trailer or van.
Do whatever it takes to make your horse a happy traveler, even if it means getting a new trailer of remodeling the old one. Another important consideration in safe trailering is good driving habits. Moreover, since the horse can't anticipate stops, starts, or turns, he is likely to get off balance. Perhaps the worst jolt you can give him is not slowing down for dips going into driveways or gas stations. If you've never ridden in a moving trailer, try it some- time.