After 1000000's of miles in my same trailer, through about 12 states, my good gelding decided to start stepping on himself in the trailer, denting up the front wall ( He was in first stall), etc. I spent hundreds and had my trailer completely gone through ( Its only 2 years old anyway), had friends ride in the back while i drove around to see if they could hear or feel anything.......... nothing. I invested in about 5 sets of the best shipping boots known to man, he would tare them to shreds in literally 15-20 miles of traveling. Same horses around him to. No bird or insect nests, etc. Covered all my bases. I duck taped all 4 feet ( Major pain in the butt) and it took about 50 miles and he had that off , shipping boots off, and legs raw. SO I threw caution to the wind ( He is my biggest horse at 16.2 and 1300 lbs in shape) and loaded him last rather than first. It worked!!! Not one single issue in 200 miles! I guess after all these years he decided he didn't want the wall in the front. Oh well! I could have saved myself a lot of cash. My vet also runs barrels and her good ( NFR) horse decided to start kicking the crap out of the trailer after 12 years and she has to hobble him now.. SOme horses!!! 

Didnt want to be the last one out anymore lol! My horse, about the same size as yours, refused to load in my trailer first, 2nd or 3rd didnt matter, he wasnt going. We bought a new trailer its wider and 4 horse and taller, its white inside. He loads up just fine now, I put him in first and hes getting better about being made to back out, still rushes a bit but the ramp helps slow him down.. they finally decided the ramp isnt going to fling them off lol! Had 1 horse try to jump over the ramp while loading for the first time. These horses .... I feel your pain lol! Glad you got it figured out!