This has been mentioned before in other threads,especially by Jim (cpaharley) but don't ignore the drain holes and window tracks of your sliding windows. After a recent downpour, we had a wet right rear cushion in our 21. I checked the window track, to find some debris clogging the round drain holes on the bottom of the track. Rainwater was not able to properly flow to the outside, and instead backed up and dripped down the interior wall. If dry, the drain holes would easily clear with a vacuum. Mine were wet, so a turkey blaster in suction mode worked well.