[kach22i]

As a guy with a pickup truck which backed into a pole because my passenger was distracting me by throwing his arms around wildly and yelling/laughing like a maniac (I have some "fringe" friends), and as a guy which was just sitting there at a stop light when the idiot behind me thought the light had changed and crushed my rear bumper a second time - keep the rear bumper intact.

Do you have a belly pan or something which would begin to warrant removing the rear bumper?

I can see cutting slits or drilling holes in the rear bumper to relieve air pressure, but doubt you have anything resembling clean air flow under the truck.