What I would do is to have someone drive for a short way for you, and ride in the trailer so you can see what's happening. It can even be a dirt road or something so it's legal, just make a few turns and stops etc. to see what's happening. But, your trailer is a 2-horse, and it'd be dangerous to be stuck in such a small place with a horse that could be falling down. So, you could either borrow a bigger trailer so you could ride back there and not be trapped so close to your horse if he starts thrashing or something; or stand on the fender on the outside of the trailer and watch through the window. Either way is good, (as long as you trust the driver:) ) and you could see exactly what is happening with your horse.