Thanks for all your advice guys!!
I actually loaded him in the trailer yesterday after I had ridden him and we stood in there for a moment and I talked to him, then I used the thing I been working with him on, I put my hand on his chest right below where his neck becomes his chest, and I don't push, my hand just stays there and I just repeat 'back'.
The first time he stepped sideways but I put my body in the way and he ran into me so he thought it was his fault then I took it one step at a time and he backed right out of the trailer!! I was so proud!!
I wasnt touching anything other than his chest, I didnt even have the lead rope in my hand!!!
it makes me feel so happy that he trusts me that much now!!!
I also got to tell off my uncle so I am triple happy right now!!!!