imo, id get it all done, sand the sides down smooth, and see if it flexes. id pour some resin on the inside - maybe try and put some matte down on the inside, and see if it flexes. if it still flexes, get some nice thin (like 3~6oz) WEAVE cloth, and first coat the pod with resin, lay the cloth down, then cover that with resin until it becomes translucent.
do that wherever the panel flexes. but you dont need it to withstand TONS of pressure, because tis just a 6.5" speaker at most right?
id be more worried about somone actually kicking or steping on it while entering the car than it not being strong enough for the speaker //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif