For those of us that may not know your floor plan can you post a copy of it. From your description it sound and not knowing your floor plan it sounds like there are leaks everywhere.
First thought would be how is water from filling the tank getting to the top of the floor unless the fill hose or the vent hose directly behind the fill port is leaking. Beyond that the fill hose should convey all water below the floor level.
Are you removing the vent cap at the fill port when you fill the tank? If not you are creating pressure in the tank that could force water up into vent hose and thus leak at the top of the vent hose.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles