I don't think my horse needs more training I just think that one time was more of a misunderstanding of what I was asking him to do. All my horses are comfortable on trailers. And I had the back of the trailer open so he just took that option lol!
Yesterday I was at a show and I had people with me but I wanted to try to load and unload alone. I had the extra set of hands to make sure it wouldn't turn into a bad experience and a loose horse at a horse show and I followed the advice and it worked great. To unload instead of pulling on the tail I ended up having my hand on my horses bum to give pressure ( she wasnt leaning on it) and then I took my hand off and said "come on" which is a habit of mine to always say when unloading and it worked great. To load I did the back bar up first. My horse was a little confused but she was tired and went with it so it was a good experience!
I have chest bars in my trailer as well, they are right by the man door which I have on both sides. One for each horse. Those bars I always keep up, Some people when they have their horse in my trailer take them down and I saw a girl do that and her big draft x jumped out the man door. If those where ever down trying to load on your own I think the horse may just do a little loop up and out of the trailer! Lol