Lay the fiberglass sheets on top of the box enclosure. Cover the surface and back if you desire. Make sure the fiberglass is taught and stretched across the surface. Staple the fiberglass to the box using a hand held staple gun to ensure a proper fit. Then cut and trim away excess fiberglass at the corners and around the speaker wells. Set the whole box on a tarp or protective cloth.

Mix up a batch of resin with hardener.Hand-held Enclosure  Read the instructions printed on the hardener for the appropriate mixing ratios. Adding more hardener will increase the speed at which the fiberglass cures, allowing less time to apply the resin.

Brush the fiberglass resin onto the sheets using a paint brush or roller.Hand-held Enclosure  Cover the entire sheet with resin, enough to allow it to seep through the weave and contact the surface of the speaker enclosure. Allow the first coat to set and dry, then apply a second coat if necessary. Allow the fiberglass resin to dry and cure overnight. It should be hard to the touch.

Sand the fiberglass after it is completely dry with a block sander and 200 grit sandpaper. Sand the entire surface smooth, removing the bubbles and ripples in the resin. Wipe the surface clean.

Apply a fiberglass primer to the surface of the fiberglass and allow it to dry. Then paint on a top coat of fiberglass paint to finish the speaker box.