I had problems with my greenie when we fist started showing, and I can tell you
HANG IN THERE
It took forever to even get Bex to put a foot in! It gets way easier as you practice more and more.
What we did, a week or so before a show we had to trailer to, we fed him every meal INSIDE the trailer. Meaning, up at 7, feeding grain in the trailer once he is clipped and latched in. Lots and lots and LOTS of praise for getting in, and then his breakfast. Then at 5, repeat the process. Everyday! It took a lot of patience but now he loads like a dream and no more fights and no more nervous horses.
The winds of heaven is that which blows through a horse's ears.