It sounds like he just needs to get out more and see more things, aka more miles.
You'll find that if you just keep being calm, not getting worked up, (it sounds like you're doing a really good job of that right now) and continue taking him out on the trail regularly, he'll get less and less spooky as time goes on.
It might also be beneficial to do some trust building exercises since the more he trusts you to "take care" of anything scary, the more comfortable he'll be on the trail. I can't think of any trust building exercises off the top of my head but maybe someone else can think of some.
Two things that just came to me are:
If you can, I'd take him for hand walks near things that are scary so he can examine them visually, and however else he wants to look at them, and realize that there isn't a reason to be scared.
Introduce him to lots of things that might be scary. Tutus, helium balloons, shiny things, plastic anything, spray bottles, umbrellas, buckets jostling around, things falling off of him (plastic containers, buckets, balls, etc), and so on. Obviously start with something little like plastic and work your way up to things falling off of him as he gains confidence in himself and in you.
The one thing you never want to do (it doesn't sound like you're inclined to do this but it's worth mentioning) is punish a spooking horse.
I did this on accident with a horse I rode in the past. He was kinda a jerk horse and he'd try everything he could think of to get to go back to the barn so obviously I read his continual spooking to be him trying stuff with me. I started smacking him with the crop every time he spooked and by the end of a week or two, he had gone from little baby spooks to really big ones. I managed to fix it but I had never thought about how I could actually make a horse spookier just by punishing him...
Another thing to consider is how much exercise does he get? My mare (also an Arabian) is oh so spooky when she has too much energy. She has to be worked at all three gaits for at least an hour three or four times a week for her head to be screwed on right (and she's in a large 3 acre pasture 24/7, I'd be terrified to see what she's like stalled! hahaha). I like to lunge her a bit before going out on a trail ride so the "edge" is taken off and she's been reminded that I'm a good person to listen to. Then when we go out on our ride, she's still listening to me well and not nearly as spooky as she would have been if I just hopped on and went for a ride.