If the water tanks are right above the bay that you noticed moisture I have 2 thoughts, both have happened to me. You might have to remove a panel to expose the tank.
1. The fitting that is drilled and glued into the tank for the supply line to connect to has a problem. We tried everything to correct it but to no avail and had to have a new tank and fitting installed. We believe the problem was caused by the tank shifting a bit and that caused the seal to leak.
2. The sensors that monitor the water fill level leak. All the sensors are drilled into the tank at different levels and the middle one started leaking. All I had to do was tighten the fitting and that secured the fitting.
Hope this helps and good luck. And I would check all fittings that connect the tanks together and any fittings that have water lines connected to them. All have the possibility of leaking.