Cliff,
I have a club cab. It drove me crazy too, but I removed the rear seat, front
seats and the entire flooring. I then removed the side panels in back. I sat
in the truck during a rain storm and discovered water leaking from under the
rear window. I removed the rear window and reinstalled it with sealant as
well, but the leak was still there. When I looked closely, I discovered that
the rear window is mounted inside a double panel that extends right up to
the roof. The outer and inner sheet metal cab panels are spot welded
together as one assembly. However, the cargo light is mounted between the
two panels and when the light leaked, water entered the area between the two
panels and flowed around the window and leaked below the window, initially
appearing as a window leak. In fact, the side of the window that the water
stream appeared on was a product of the level of the truck, so the dampness
would appear on both sides depending on how you parked the truck. The water
would then make its way forward on either side as the center of the floor
panel is raised in the center directing the water to the forward seating
area.
Steve