Pivoting Headache Rack: Anybody Done It?

AdaRac has some pretty robust right-angle rails along the bed's edges.

I'd like some passenger/driver protection in the event of a minor crash and a Skil saw, router, generator, hammers, or whatever else I wouldn't care to take in the back of my neck at 30 mph.

Seems like something could be worked out that pivots on the AdaRac's rails. Mockup at:

Flaws in the basic concept?

And I'm wondering about a suitable material: something that will absorb the energy, yet not be too massive for somebody to flip up and down by hand.