One thing you don't mention, and may not yet know, is whether he is really sleeping any better in diapers than without them. If he is now able to get a good, restful night's sleep without worrying about a wet bed, but had always had that concern before, it may not be a good idea to retrain him just yet. Rather, I would have him checked out by a urologist, and possibly by a therapist. The urologist can find most medical problems, if there are any, and the T can deal with anything upstairs that may be interfering with a dry bed.