there is a definite difference in horse size and trailer size
. What you need is a turnbow thoroughbred walk through trailer
. I'd get a 2 horse WALK THROUGH THOROUGHBRED straight load side by side TRAILER normal 2 horse in other owrds not a slant load. I Recently bought one for my 16 to 17hh horses and IMO it is a MUST for bigger horses. Not only is it taller (I'm 5'7" and I can't touch the top with I stand inside) but it's wider and longer too. Horses do not like to walk into a dark small cave. My trailer has plenty of windows in the sides and in front to keep it light. Plus the back door pulls down and works as a ramp which a lot of horses like.
I rented a 3 horse slant load TO GET MY HORSES HOME and it was a nightmare.
the fit was way way to tight side to side and they didn't have enough head room either and that was a trailer that the rental place TOLD me was for TBs.
My trailer cost me 2000. Used it's really nice but older. You can find the small ones all day long for 1000. But ill tell you if you get your horse into that trailer once and he's uncomfortable you will never get him to willingly go in again. Just my 2 cents good luck :)
PS check out around the race track if you want a trailer for TBs you will find one for sale there that will work great for your big guys :)