I want to make a suggestion to change your approach slightly when he reacts. Instead of making him work around the object of his spook, try making him face it and walk towards it. Every time he turns in a different direction then make him work tight circles and release him in the direction of the object. Ask him to move forward towards it again and keep this up until you can walk up to it to the point he is touching it with his legs. Even have him step over it if possible until he is completely relaxed while doing it. I will add that you must be absolutely calm during this, because if there is an ounce of nervousness in your hands or body, it will transfer to him immediately. Don't have the mindset of "what is he going to spook at today", instead have your mind made up that it is going to be a good ride and if something comes up then we will work on it UNTIL IT IS CORRECTED. If you start and do not finish then they learn the boundary they have to reach to outlast you.
Do that exercise with several different things he spooks at and see if it will calm him, but remember this will only work if you stay calm, confident and in control. I had to do this with a couple of mine that spooked at simple things like a high chair someone had out by the road to be picked up. Another time was square bales of hay at the end of the road where the county worked on the drainage.
Pointed him at the high chair and asked him to walk towards it and as soon as he wanted to turn away from it we did about 6 tight circles then came to rest facing the high chair again. We did this until he walked forward and had the high chair actually rub his side as we went past it. Then walked back and forth past it until he didn't even look at it.
Same thing with the hay bale until he was stepping over it. I do not usually work this way as I try to spend enough time on ground work to get them to trust my directions so they are focused on me instead of their surroundings. I hadn't had him long and this was our second ride outside of the yard so I decided to use that technique since I was there and didn't want him to win at not going forward. We would have been there all night before I allowed that to happen.