Also, you need to keep in mind that whatever you place back there will also sit atop the load floor (panel for the spare wheel). Make sure any weight is properly distributed across that panel. If weight is centered on the panel there is potential it will sustain damage or permanently bow in its center.
I'm only indicating this because I used to work in a test lab and they did testing on these floors of both Durango and JGC. We would place weight at different positions and also run them through hot/cold environmental changes with the weights. Many times the load floor failed by bowing or even no longer latching shut with weight reaching around 200 pounds and higher. Temperature will also play a major role with this. Hot temps will make it easier to deform. Colder temps made the latch connection break or not function correctly.
Remember, this is with weight applied. When the weight was distributed across the panel the failure weights significantly dropped.
The weigh capacity for in/on vehicle cargo (including humans and tongue weight if towing) is published in your manual as well as in the online specifications. As long as you don't exceed that in combination, you'll be fine.