ok, its kinda like bondo, but its fiber glass. whats the difference of what you use to block the duct off with? you could use wood if you want, but nobody will see it over the duct.
I tokk my trusty Dremel and cut all that shit out of the way, sanded down the bezel, taped a piece of tshirt over it. then i layed a thin coat of fiberglass resin on the shirt. let it dry. just a thin coat though, otherwise it will sag on you. Then after thats dry, add another layer of resin. i think i overdid mine, but i added another piece of tshirt, and like 3 more layers of resin. i think if i hit my head on it, it'd be harder than the windshield, lol. Punch the holes, paint it up!