Ok I understand now a little more, this is the issue. Your floor sits on top of a corrugated plastic cardboard. You can see it from the underside of the coach. Water is probably making its way down to that layer through a leak from the wall It then travels to the low point which must be behind the passenger seat. What I would do is try and figure out what the attitude of the camper is, is it listing to the passenger side and down by the bow (front). This would allow the water to travel towards that direction if it were leaking from the drivers side etc. You can also remove the transition strip between the carpet and floor material to see if that helps determine a direction of the water. If you get an idea of direction the water maybe traveling from then walk around the outside and take a close look at the hardware screwed to the walls on the outside, ensure it is calked up. I used calk tape (butyl tape) under the hardware and then used clear silicone at the top of the hardware. I did both sides of the coach even the little clips that hold the compartment doors open.
I hope this helps,
Lance
