Where did the water come from?
We had a puzzling experience recently. We had a weak spot in the floor, near the front of our 2006 23ft corner bed unit. We were able to patch it pretty nicely using Marine Grade plywood. But the patch isn't the reason for my query, the source of the water is.
We have owned the unit since 2012. We recently removed a section of the floor and found a small amount of water on the foil vapor barrier under the wet plywood subfloor. The vapor barrier looked very much like the puffy foil sheets you put in the windshield to protect from the sun and it was totally intact. Beneath the foil was a perfectly dry and clean (no rust) open space. You could actually stick your head down there and look all the way to the back of the unit, and it looked very clean and totally dry.
So now to find the leak. First we read several threads on water and thought maybe there is a leak in the public or interior water lines...no luck...it held 68 pounds of air overnight! We didn't want to put that much pressure on the system but once we pumped it up we just left it.
Next we figured a window leak, or a leak in one of the roof fixtures. Found a post where the owner used a "bounce house" fan to test it out. My friend had a contact and we were able to borrow a fan used to test pressure leaks inside houses. We blew air in through the storage door, and it rushed out the door when we opened it, but lots of soapy water around windows, roof vents, AC, etc., showed no sign of leaking.
We have one remaining possibility which is somewhat mystifying. About ten (yes ten) years ago while traveling in Canada with a full tank of water, we left the pump on, and the kitchen sink handle toggled on, the dishpan in the sink acted like a drain plug, and we ended up with 20 or so gallons of water on the floor. Of course we mopped it up, and "dried" it out at a Provincial Park for a couple of days. Never gave it another thought until now.
Is it possible that some of the water from the episode in 2012 could have been contained between the vapor barrier, in the plywood subfloor, and under the vinyl for 10 years? There is no indication of water anywhere else except the front of the unit about even with the door and in one corner of the nose.
And, when the bubble on the side says we are level, a 4-ft level on the floor shows the front is about 1/2 inch lower than the area in front of the kitchen sink...which would indicate that any water spilled on the floor would tend to run forward under the couch.