Fiberglassing Door Panels

Me again, 1993 Firebird. I am just curious if anyone has tried to fiberglass a Firebird/Camaro door panel, because the top part of the door panel is used for weatherstripping. It has a single speaker housing in the door, which is just a grill covering the door speaker. I plan on taking the door panel off, mounting my speaker ring for a Kicker ss 6 inch midbass, then stretching fleece over the panel and coating it in fiberglass. Also, I see people putting multiple layers of fiberglass over, why is this, because the original door panel should have enough strenght, and most component speakers are not heavy enough to require more than one layer of fleece. Anyways, your help would be much appreciated, you'll see plenty of posts about my car, as its going to undergo one hell of a stereo.