Good article in Equus this month entitled Reform Your  Problem Hauler.  The article was written by Jennifer Williams, PhD.

Reading the article alone won't help a problem loader/hauler but there is some good info if you/your horse have that problem.

roll on

I read in Naturual Horse in a long ago issue that some people had a problem horse when trailering--it scrambled violently when they turned to the right to the point it would put its hooves on the side of the trailer wall and hoist itself up on the divider panel.  (straight load). 

The owners didn't haul the horse after that, but becasue of another issue that the horse had, took the horse to a dentist who was at another barn who had a very good reputation (the horse also had problems chewing)  They were afraid that the horse would get injured but realized it might help the chewing problem and decided the short ride probably wouldn't cause too much trauma to the horse.

After the dental work, they waited a reasonable amount of time after the trank wore off, loaded the horse and they found that he no longer scrambled in the trailer and rode quietly. 

It had to do with the way the jaw was locking on the horse and when they turned to the right, it was worse because the horse somehow couldn't use its neck to balance because the locked jaw caused a lot of pain for the horse to use its head properly in the balancing, so he just would prop himself up on the divider.

So sometimes, training helps, but there can also be a physical problem contributing to the issues.

Jbsny