Greg,

Ask a body shop supply company for Corvette Panel Adhesive, An epoxy
material that has the same sanding characteristics as the fiberglass
body panels and bumper covers is best for the finish.  Use short strand
fiberglass patch for structural reinforcement.  Also use a scrap
bumper/panel pieces to back up the crack or damaged area by 1/2"
overlap, just glue on with the panel adhesive.  If the damaged area is
contoured, either use a similar contour from scrap, or use the short
strand fiberglass filler.  I cut the piece to shape with a Dremel and
the cut off wheel.

Sincerely,

Mark Keller