One thing I've been considering, and am in the process of preparing to do, is to build a shelf/storage area in the back that's the height of the seats when folded down (not folded forward though). Downside to this in your case is it counters the slope b/c the seat folded forward does not lie flat-and even if you're short like me you're not going to be stretching out all that much. Purpose in my eyes is to give someone a place to lay out during long trips and get some kind of rest.
The shelf itself would be a simple platform, open to both the front and the back and closed on the sides (jumpseats are being removed for further storage) and I would likely put carpeting on the shelf to match the truck's tan interior.
Overall vision is to get an Engel for the back left side so that the 60 portion of the seat could get folded forward but leave the 40 side as a seat with the Engel directly behind it-thus room for a somewhat comfortable single individual to catch a nap while the other person drives.
Clearly I'm still in the stages of opening up my back door, looking at it all, folding the seat forward and deciding "wow, I'm short but that's still not much room" and such...
Just figured I'd throw it out there as a way to keep your seats and make some functional space in the back for the 95% of the time we use our trucks not in expedition mode (or at least the unfortunate 95 + % I do).
r-
Ray