But, uhhh did you close up the bottom layer back at c-pillar? I did on G3. But on 2Ghetto I didn't.
Dust, etc can still get through because that internal hump isn't sealed for shit. It has considerable openings into that open space of quarter panels(for stock rear seats and jack) on both sides. Take a gander. About 2" tall and finger wide hole in back corners of hump that open to the pocket area. Mine also didn't seal well along the top of that vertical ridge that separates hump from pocket.
I just addressed this the other day with 2G. Easy fix should work. I just made some small 18 gauge plates with 90* bend. Tacked um in to cover holes that go to pockets.... and sealed the shit out of the seams with a bunch of RTV.