Something behind the rear valance?

[neokpd]

Recently Nightmare went sideways and took out a mailbox. It now needs the rear fender flares, rear valance, the passenger side inner fender cover, tail lights, and a front muffler. The insurance inspector said that with the amount of damage done, the major factor in totaling it or not would depend on whether something that can only be seen by removing the bumper could be examined.

I want to say he called it a tub? And seemed to believe it to be made of fiberglass and is apparently very expensive to replace/repair.

Does any body know what he may be referring to? I've been searching the forums and google for hours and still don't have a clue. Thanks in advance