Thanks for the replies. His previous owner was unloading another horse first, when Ed got upset, broke his halter, flew under the butt bar, got really torn up, needed stitches - I'm guessing on his hind. Ever since then he flies out the trailer backwards.
This horse is trying so hard to please. I know its not about the trailer, its about leadership, trust and confidence.
I've made certain he is light and responsive for walk on, whoa, backup commands as well as leading well. He's been very good backing up and navigating in tight spaces around barrels, etc. He'll yield his hind just with me pointing, or back up with my index finger wiggling at him. Today he got into the trailer, all the way in, 3 times, and no poops!
He's got an anxious side to him, because even if you ask lightly, he'll rush his hind quarters over when asked to yield. So I'd like him to relax and slow down. I believe we'll get there, its just going to take some time.
As he progresses, I am going to keep asking for guidance. Right now I just want him to relax in the trailer, I ask him to pause, then back up, perhaps one or two steps, come forward, and pause, and eat. And repeat. It's a good thing he's so food motivated.