Does anybody else have a Rhino Liner and have a problem that it stays perpetually filthy? I can't even let my kids sit in the back of my truck in the driveway without their clothes getting covered in black crud. I have a couple of friends with Rhinos and they don't seem to have this problem. Anybody else?

I've tried scrubbing the thing down and it doesn't help. After a few days, same problem.

any suggestions? Thanks in advance.