building custom box, 85 camaro

I want to build a custom fit fiberglass box for my 1985 Camaro. I built a box fiberglass/wood box for my Camaro last year and it came out great, but I want to do this one a little differently and I'm not sure how.

What I want is to have a box that fits perfectly over the humps in the back (see picture below). There will be a 12" sub on each side and the amp in the middle. I've done a lot of research and I know how to get the hump areas fiberglassed, but I'm not sure how to "connect" everything.

My thought was to use some MDF as a base, cut it to the right dimensions, put it in place and then fiberglass each side to it but I'm not sure how strong that would be. The other option would be to fiberglass the entire area, including along the floor and then set the mdf on it as it dries but again, not sure how that would work. If I don't use an MDF base, then I don't think the box will be strong enough and I won't have a base to build the amp rack off of.

So...when creating a large box like this, what is the proper way to do it so that it fits snuggly on each side but is still strong enough to do what I want to do?

I'm currently designing a custom enclosure for my 1985 Camaro. I'm doing something a bit different and I'm really pressed for space which leads to two questions:

1) Is there a minimum clearance distance required for the front of the subwoofer? The way I currently have the box only leaves about a 1/2" of room between the front of the sub and the hatch. As long as it doesn't hit when the sub moves, is this okay?

2) For the required air volume, does that take into account the volume the sub itself takes up? What I mean is, if I have a sub that requires 1 cubic foot of space, can I build the box 1' x 1' x 1' or do I need to make it larger to account for the air the sub itself takes up?

Thanks.

https://www.the12volt.com/installbay/forum_posts.asp?tid=114565&KW=camaro

Do not fire any woofer straight up into the plastic cover located at the base of the window.  If you fire a woofer into the glass, fire the woofer straight up, not parallel with the glass.  The box in the above post was a great sounding box.  Not loads of SPL, but it was a great sounding box.