[brucepick]

Building the belly pan on my '97 Civic (same generation as yours) I had to put only one screw into metal. All other fasteners went into either the plastic side skirts or into the front and rear bumper covers.

In some areas I did use 1/16" or 1/8" aluminum bar stock to create a frame. I attached the frame to plastic at the car's outer perimeter as noted above and then pop riveted the aero panels to the frame. You need washers on the visible side of those rivets because neither Coroplast nor aluminum flashing will hold a rivet just by itself.