Normally, fiberglass and metal do not mix. When they do, it is usually in an automotive or marine application and not around the house. The most common application is that of a fiberglass scoop on a metal hood. Bonding fiberglass to the metal works better than trying to attach the scoop with pop rivets or screws, covering up the whole mess with body filler and having it crack within two weeks.
Rough up the metal surface with a piece of coarse grit sandpaper. If bonding fiberglass gelcoat, rough that up too. Roughing up the surfaces give the epoxy more surface area to bond the fiberglass to the metal.
Mix up a batch of the epoxy large enough to bond the fiberglass to the metal. Follow the instructions on the epoxy packaging for mixing ratios. Mix the epoxy with a popsicle stick.