I ordered both the short and long Weathertech Cargo liners for my 03 Durango. The large one is approximately 51 inches long. When you fold up the 3rd roww seat, you only have about 20 inches in the cargo area, so you are folding approximately 30 inches of material towards the back. (You will need to fold the liner towards the rear before folding 3rd row seats to the up position).
Yes, you can fold it but if you need to put anything on the back, you need to lift the 30" or so of material in order to put your items directly on the cargo area. I decided to keep both the short and long version. (If you need pictures, let me know).
BTW, they look nice.
Also, if you purchase them for the front driver/passenger area, make sure you order the ones for the 2013, as the 2011 and 2012 only has one carpet hook on the passenger side and two hooks on the driver side. The 2013 has two hooks each on driver and passenger (don't ask me how I found about this
If you need additional information, let me know.