I have not seen a custom cargo liner made to fit the back with the rear seats down. I have the Rugged Ridge cargo liner, I keep my rear seats folded down all the time and I use a cut-to-fit liner for the area not covered by the Rugged Ridge cargo tray. It is not the perfect solution because the Rugged Ridge tray has a fair sized lip that can snag things you are trying to slide into the cargo area, but the cut-to-fit mat does a good job of protecting the back of the seats when they are folded down. You might be able to find a cut-to-fit liner that would cover the entire cargo area. This is the liner I am using, it is pretty good, quality-wise:
[ame]http://smile.amazon.com/gp/product/B00CAKILAO/ref=oh_aui_search_detailpage?ie=UTF8&psc=1[/ame]