Pardon my alliteration.
This was quite disturbing.
We have a dinette, and under each bench seat is a drawer. For the past few months, we have stored our Glad-ware in the drawer that abuts the outer wall. Recently, I noticed mold inside the drawer along the back and outer-wall side of the drawer. I cleaned it and attributed it to not drying the Glad-ware well enough. The drawer shuts well and I figured not enough air was getting in...creating a nice, warm, dark, moist environment for mold.
Paying closer attention to drying the plastic containers better, I thought the problem would rectify itself. But, soon an odor started to permeate from the drawer when opened.
I opened it up as much as I could and once again saw mold. Upon emptying the drawer, I could see the mold was all the way to the back, once again. Now, in their infinite wisdom, Jayco made it impossible to fully remove the drawer as pulling it out all the way causes it to hit the opposite wall stopping any more movement.
Using a flashlight and looking through to the area behind the drawer I was shocked to see a forest of fluffy, cotton-candyesque mold growing. Grabbing the phillips head, I removed the plywood board under the seat cushion and started cleaning.
The wood was now dark and slightly warped so I put the heater to task.
No more storage of possibly-wet items in this drawer. IF that was actually the issue. Hoping it was. But another theory is that moisture from the window just above the bench (which tends to allow rain water in (dripping quite heavily from the awning above) if we don't shut it quickly enough) might be the cause. Other times, condensation has had that window and wall beaded with water which may have dripped down behind the bench seat.
The carpet underneath was not wet, which was a relief.
Considering this RV is a standard set up with dinette on the slide, keep an eye on that area under your bench seat. And don't use it for plastic containers!