Usually i earn the trust of a horse when we both make positive experiences together.
When he spooks somewhere take your time and really calm down and make sure you are able to walk there with your horse after some time.
Everytime he follows you and nothing "bad" happens to him ( what he probably thought would happen otherwise he wouldn't be spooky) he learns that when he follows you, nothing bad will happen to him.
Do everything with your horse even if it is difficult and even if it will take time and if it will get on your nerves - take your time and tell yourself everything will be fine in the end.
Never say: I can't go there and I can't do that because he is spooky.
Then he will stay spooky
Always take your time, never force him to do something he is afraid of.
He will probably do it for the moment but after that he will never do it again
Step by step.
Before going to the shows put him in the trailer and go somewhere else for training. In this way you make sure that you won't be a tiny bit nervous and you will be able to give him the safeness that he needs from you.
Every good experience that you make together will increase the trust between you two.
my horse was spooky and super crazy when I got him and he is now going everywhere with me and follows me like a dog without headcollar.
Spend a lot of time with him, play some music and give him some nice long grooming sessions, clean equipment outside his stable door so he can see you, let him follow you around as you check his paddock... let him get to know you in a no pressure environment and take the riding easy at first til you understand each other!