Chinook RV

We took our first camping trip last weekend. The two hour ride up was a full on gully washer. It rained so hard, we had to do 40, and there were multiple cars in the ditches from hydroplaning. It rained slow and steady that day, and part through the night. The next day was dry. I noticed some moisture under the drivers side floor mat nothing crazy, like puddles, but there none the less. I didn’t get in and out of the front, so it wasn’t from rain coming in the door, or from wet feet. I let it dry out and it’s been dry since. Is there any connection or hose in any of the systems that would leak/drain there? I just, first, want to be sure it’s not something like that. Aside from that, I’m not sure how else it would have come in, but maybe so much splashing up from the bottom somehow?

There is about a 2” rubber plug under carpet below brake petal, if it is loose it could let water from front wheel splash in. I removed mine when trying to get wrench on top nut of shock. If someone did this it’s possible it was not reinstalled correctly.

I have not experienced this on my Chinook (yet), but a friend had this same symptom on his 2003 E-450 other-brand Class C (same cab as ours). I did a bunch of research and found mentions of scary things like inaccessible cowl welds. I also taped off sections of the windshield and cowl area and then tested with a hose.

Ultimately, we decided the windshield was the most likely culprit, and even if it wasn't, being 15 years old hadn't done it any favors in the optical quality department so it wouldn't be a total waste if it wasn't that. He had the windshield replaced and no more water under driver's floor. Still dry 3 years later.

I had this issue with my 2001 Concourse. No "flooding" but annoying damp/wet spot at the left side of the footwell floor.
I traced the leaking to a couple of likely sources:
Driver side cowl vent/firewall access holes with deteriorated rubber plugs
Windshield gasket separating at lower driver side corner