Thank you all for your inputs and suggestions. I will now always shut off the campground water when leaving for any extended periods. The water never overflowed the shower pan itself, so I had no water damage inside the coach. Additionally, I never found the small leak on the outside. Don't know if I had a small leak near the top of the gray tank or a line. Since it did not cause any harm, it did not warrant the challenge to remove the front panel on the outside water bay for investigation.
Dave & Kathy Cramer (Full Timers) AF CMSgts, Ret
2007 Monaco Knight 40PDQ
2003 Honda Odyssey, Toad Stop Braking System