I feel your pain! I have a 17-3hh Holsteiner and I am in the process of buying living quarters. Slant loads just don't work for the big horses. I was lucky enough to find a great price on a straight load LQ, but I did consider converting a 4H slant to a straight load for my special needs big boy.
I currently have a Collin-Arndt 2H bumper pull warmblood sized trailer. I have had no problems with my Holsteiner or my mother's old 18-2hh percheron. Collin-Arndt has been purchased by Shetron, but it's the same basic trailer. Great product for the price!! And the best part is they will build it custom soup to nuts for you for the same cost of an off the lot name brand trailer. You can order from the factory and they will add length, height width whatever and where ever you need.