On the 2015 Cherokee Limited the stop bar slides under the front lip of each seat track. You have the option of keeping it temporary, which means you install it before each tow, or mount it permanent by screwing it to the seat pan through the pre drilled holes. Once you install the stop bar and then the RVi Brake, the box presses against the bar, it can't dislodge. Granted, this is for a Cherokee Limited, but your Grand Cherokee will probably be very similar.
Bill & Denise
2014 Bay Star 3103 - 5 Star Tune
2016 Jeep Grand Cherokee 4X4 Limited