I have a 2 horse slant that has one big door in back. It doesn’t have any chain, divider, butt bar or anything except the rear door. I don’t know why they make them that way.
I have a 2 horse slant load without a rear tack. Back stall has no butt bar/chain. I haul horses in that stall a LOT. When we get to our destination, I untie them (through the drop down window) and then I go around and open the door. They back out after the door is open and I grab lead rope as they exit. Never had a problem, except for 1 mare that is not very good about unloading (she turns around instead of backing out and is always in a hurry to get out of the trailer.) I quickly learned NOT to put her in the back stall. She goes in the front stall and we have an unorthodox method of unloading that works perfectly for her. Every other horse has been fine.
My trailer is a step up though - not sure I would be crazy about that set up if I had a ramp that didn’t also have full doors. I wouldn’t want to risk getting squished by the ramp when a horse wanted to hurry out! That does seem rather dangerous for the human.
I never have help loading or unloading at home so my horses and I have had to learn to deal with it.
I will say the trailer accident linked above certainly has made me think about a horse in my back stall. But, the closing mechanism on my rear door is MUCH more secure than the one on the trailer involved in the accident. I really appreciated the write up about the accident, however. I have been looking for a LQ trailer and have ruled out several brands due to the way the back doors latch.
KR- a trailer dealer might be able to add a telescoping rail divider for your last stall- it would not need a head divider but rail shoulder/hip high with half bar to the ground. You could attach a stall butt bar/chain from that to the right wall.
I witnessed a horrific unloading accident one day. The national level trainer was unloading a horse from the first slant in her 3 horse trailer. She opened the divider and clipped on the lead rope. The horse heard the clip and thought it was the second part where she unclips the horse from the wall. So he started backing out, all 17.2 hands of him. He hit the end of the short tie rope, went up and down, up and down, each time hitting the top of her head with his chin as he struggled until she was knocked out cold underneath him. She ended up with surgery to repair damaged disc in her neck- like 3 vertebrae. It was horrible to witness. Again, it was NOT a bad horse, just a situation where the horse thought the sequence was at the “exit” point and acted on it. 
You can never over train a horse to be patient when loading and unloading from a trailer. I use Blocker Tie rings in my trailer with dedicated cotton lead ropes. If for some reason the Blocker Tie ring fails a cotton lead rope can be cut much easier than a nylon lead rope- a built in redundancy. But most of all I teach my horses “wait” and then “back”. They are unhooked before the divider opens because if they are going to blow up and scramble out I want them to get the hell out of the trailer and away from me so we can live to train out the vice another day. I am an amateur owner and completely driven by using safe handling techniques.
I got a private message from a trailer dealer explaining how to add a butt bar. I believe I will show this to our dealer when I take the trailer in for it’s annual maintenance next month.
SLW – I follow your instructions “to the letter” every time we trailer. Thanks for teaching me safety!
Blocker tie rings in the trailer - that is a good idea. I have used them to tie TO the outside of the trailer but never thought of using them inside.
And definitely untie the horse BEFORE opening a divider or door. Although I have accidentally forgot this step on occasion. My horses just stand there and look at me like “well, idiot, are you going to untie me so I can unload?” But, you never know what might happen one day that panics your horse and as you said, you want them to be able to get the heck off the trailer and away from you!
