This may seem a bit harsh, but if all else has failed, it might be worth a try...

It sounds to me like its an attention seeking behaviour - any attention is good attention in children who have emotional issues. He's obviously capable of stopping himself from wetting the bed (ie when he knows something good is around the corner for him - school camp!).But the fuss and upheaval that he can create when he DOES wet the bed is ensuring that HE is always the centre of attention in your family. Sounds kinda weird but it does have a thread of sense to it. I would be trying to ignore it - let him know that he is loved and a valued member of the family etc etc...but from now on its HIS problem. I know you said he already deals with the laundry but make sure that you absolutely don't have anything to do with him wetting/cleaning up the mess. Tell him "you know where the pads are....you know how to set your timer....you can take yourself to the toilet....and stop drinking after X time....you're old enough to sort yourself out" (along those lines). Are you able to have a discussion with his psychologist about this kind of approach to get their opinion Or at least to clue them in on what you're trying at home?
A little bit of 'tough love' can sometimes work wonders. I'm not advocating emotional abuse or that you set out to give him even more psychological scarring. But it seems to me like you've taken all the load for a long time, it's sending you balmy!...so maybe he needs to take this on fully now.
I dunno....it's just a suggestion...