R.G.
R.,
There are a few homeopathic remedies you can try to help strengthen his bladder. Hylands makes a good one.
You might also want to consider having him adjusted by a chiropractor who's familiar with treating children. This can have a HUGE and positive impact on staying dry at night. It worked wonders with my daughter who was completely dry and began to regress for no apparent reason.
Best of luck!
Blessings,
Rolinda
Wife, Mother, Friend