When they change the body style for 09, they did away with the flat storage for the rear seat. The older quad cab fold flat platform will not fit in the new body style. I wound up making one out of a piece of 3/4 Advantech and a couple of 2x4's, covered it with carpet to get a flat area for our dogs when we travel.
I thought the body change was for '10? Did it change in '09 or was that late '09 when the '10 model went on sale?
Ain't Dodge confusing... my 2009 4500 is 3rd gen body style w/ single foldup bench in back that I installed the fold-flat storage into.
Since your's is 4th gen, I would think 4th gen fold flat floor, if offered, would work with your 4th gen.
Wiredawg