I didn't remember this and a quick scan of the GCR has me wondering what rule you are talking about.
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I think he's referring to this verbiage:

In any automobile where allowed removal of rear seats, upholstery, etc., creates an opening between the driver/passenger compartment and an exposed gas tank, fuel cell, or part thereof, a metal bulkhead which completely fills such opening shall be installed (See GCR 9.3.26.1.)

This is from 9.1.3 E in the IT portion of the GCR. In Civic/CRX's the removal of the interior panels or rear seats causes the fuel filler neck to become "exposed"...

Christian