This is the type of stuff I take my Cummins through:
YouTube - Illegal Wheeling 2
Between and above the frame rails doesn't really protect it. Cast pans crack and leak all the fluid, steel pans dent - obviously neither is good. I have a full cage underneath. But a cage wont always protect the full weight of the truck on a boulder.
In my daily driver Ram, a cast pan is fine and perhaps preferred, but in a real offroad enviroment where you may kick up a rock between the rails, a cast pan is a definite no go. I still have a full cage over the pans and tcase and they still get impacted.
I actually spent time and $$ to replace a cast pan.
Just my . 02