he fiberglassed inside the box i believe.
but yes, fiberglass mat will strengthen the enclosure. an easy way to look at it is to consider the two types of forces, you have compressive forves, which push the material together, and expansive forces. the matt will help strengthen the expansive nature of the enclosure, keeping it from wanting to asplode. but a large majority of the overall strength and the compressive strength comes from the resin itself, the matt helps by holding more resin and adding expansive strength.
p.s.--i know compressive strength and expansive strength isnt the right words... i just cant remember them at the moment //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
p.p.s.--acidburn beat me to it. //content.invisioncic.com/y282845/emoticons/toast.gif.bc0657bf54b9ee653b6438524461341e.gif