I don't know of one that mounts while keeping the seat. The seat sits so close to the wall, I don't think you would be able to mount much to it when the seat is up. I believe, unless you screwed directly into the plastic, the mounting points needed may also interfere with the seat. It may not be impossible, but I'm not sure you would get much use of it with the seat up.
I could see someone wanting them there for when the seats are down.
Could even put on color coded quick fist mounts when needed.
I guess it depends on what installs faster for a weekend trip.
Because there is not much space behind the seat.....not seeing the value of the addition. Unless you strip everything off the back wall under the rear glass, but not certain that would provide much usable space
I know there's one that covers the rear window, with the exception of the Slider. But, I haven't seen one for behind the seat, with seats retained. Blue mountain Overland makes bags with velcro that bo behind the backseats.