Well, here I am with a comment but not directly related to your question because I don't know

BUT I was driving beside an empty aluminum horse trailer and it was bouncing around all over the place and LOUD. It started me to thinking about the weight of a trailer and its stability. It was one of those stock trailers that could fit up to 6 steers or horses in it, two compartments. And I'm thinking that those 6 horses would weigh more than the trailer empty. That can't be good. Because the horses could move enough to destabilize the trailer. No thanks. So I wonder about the weight difference of the two trailers and how that compares.
My husband is a welder and we were looking at those fancy-schamncy ones with the living quarters in them and the welds were not very nice in the horse part. They had sharp corners. I'd look for that.
Gerald says that the slants are easier to get horses in and out safely for the person, who isn't stuck in there with a horse. That's a good feature too.
Just my two cents.