G.F.
I had a problem with bed-wetting until I was about 8 or 9. I had an alarm, but I was such a heavy sleeper that I would not wake up for the alarm but the rest of the house would. I don't know if the alarm is what helped me or if I just grew out of it.
Ask him if he remembers any dreams from before/during the bed-wetting. I have "trigger dreams" where I am looking for the restroom, and when I find it and go pee in my dream I would go in real life. I trained myself to wake up when the dreams would start and I had a very strong urge to go to the restroom. I still get the dreams but don't have accidents anymore.
Good luck. I know it's hard on him. Do what you can to make sure that he doesn't have any self-confidence issues because of this.