Fiberglass Wrangler box

Allright so this is my first post and I just registered... I've been reading over this site for a while.

Im pretty sure that I am going to buy my dad's 99 TJ from him (he got a new car). The speakers in there are already blown and its a stock tape deck so it needs to be redone! But the restrictions of space and sound quality in a jeep are huge. When he first bought is someone sold him a box that was supposedly made and it didnt fit due to a wierd hinge on the door. I know wood would be hard to form around this. So my idea was to make a mold and then a fiberglass box.

The Mold-So i think the easiest way to make a mold would be to shut the "trunk" all up and cover everything with plastic and then alluminum foil. Then ill go buy a couple bottles of low expanding(Window and door sill) foam and fill that area up with that. Then it would seem i would have a mold that matched all contours and hinges.

The box-So now that i have the mold i have to prep it. Im thinking i want one twelve... im pretty sure I could pull off the sealed twelve or maybe even a ported 12 or 10. So i want that 12 to face the rear seat at a downward angle, that way it cant be seen and the seat wont rub on it. Then i want the top to be flat. I also have to take into acct. the thickness of fiberglass... which I am assuming will be from 1/2 to 3/4. So after all of the sanding and cutting I should come out with a mold that i can cover and then fiberglass?

Does this sound like a good idea to everyone? Sorry for the long post and thanks!

I just did a wrangler box it was fairly easy but tight. If i remember right the box is 17"tall 32.5"wide, 8"TD, and 11.25"BD with about 3"x3" cut out on the edge for the latch. It has 2 10" kicker l5's with a kicker kx1200.1 1 farad stinger cap all under the back seat. We had to raise the back of the seat about a 1/2" to make it fit. OH you have to put 11/2" riseres on the bottom of the box if you make it a down firing box. Hope i helped.