So, I went through this with my '04 and am shocked that it appears I'm dealing with this on a new 2020 Bighorn. In the drivers side storage area under the rear seat, yesterday I pulled out a soaking wet roll of blue shop towels. Had an appt at the dealer (there now) today so I mentioned it. Got the same answer I got before on the '04. Could be leaking around the rear brake light, the rear window, etc. The truck has a little over 1000 miles on it. Better yet, they say that they outsource fixing that, to some "water doctor". Can this really be happening on a $70k truck? I am well and truly ticked off. When it happened to the '04 I had to rip out the carpet, etc to let it dry out without getting mold and mildew.