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Are you connected to a shore water source..., or just water in the fresh water tank??
Assuming it's a fresh water leak, I would start looking under sinks, tub/shower/toilet, around the water pump. Some tub/showers have an access panel near the base of the tub/shower.
Also, there should be a removable panel on the underbody that accesses the slide motor..., removing it may give you a vantage point to view (with flashlight) a possible leak area.
Mositure leaks travel, so the source could be anywhere.
2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)