I saw there would be about 5 inches between the 2 items. My wife has a jlur and what doesnt fit in the bed would fit in the back of that.You don't see it because the decked system takes up such a significant amount of area in the bed that adding the diamondback would give you ... maybe 2-4 inches of space between the bottom of the cover and the decked drawers.
Is there a use case you have in mind? The decked system is supposed to be very rugged, not sure why you would put a diamondback on top of it.