It is difficult as a parent dealing with a child with a disability. Chronic pain can be and often is very debilitating.I wouldn't be surprised if this also contributes to his day to day fluctuations.
I think it would be quite normal being anxious about wearing the brace and from what you say it appears he is trying to develop his own strategies to deal with it. He has obviously accepted the treatment that is required. I am no expert as far as therapy is concerned so I can't answer to that. I think one of the difficulties children face is feeling that no one understands what they are experiencing and lets face it unless we have the same disorder we don't reallyunderstand. We do the best we can. At times we get annoyed and lose our temper, which unfortunately makes us feel even more guilty, you are not alone there.

As you say thank god for his sense of humour! and I think you are right when you say he probably copes better than most, don't underestimate that. Just one question, is he able to access a forum or association related to his disorder?