So I've had plenty of time to think about this and decided to go with two 8" subs in the side walls behind the driver/pass seats. Tis a 90 two door. I saw someone from these forums place speakers in the same spot but I think they left in the plastic trim, which I'll probably put back, but obviously with a portion cut out and fiberglass to fill voids. Working on the brackets to hold in place right now.

 

 

Ive never seen anyone put subs there! Interested in seeing how this turns out! Ive always wanted to put a 10" kicker in the cubby hole in the back but my finances say no hahaha

 

The 8" subs are the biggest you can fit in the space I chose. A ten in the pass cubby could work. The box I made was a tight squeeze, however I believe it could extend to the rear slightly. Pm me if you want a detailed explanation on how I made mine.

 

It worked out PERfectly. I added s/s tabs on the box to work like mounting brackets to mount two the frame with rubber gasket material as dampening. I'll try to snag a video and post a link of it bolted.

 

Very clean!

Yes, post finished pics - I would love to see them.

 

Ask and you shall receive.

 

Rubber gasket bxetween ss tabs and frame, rubber washers for the backside then a metal washer to keep everything nice and dampened. Fyi! The bottom left edge and top/rear edges of the box need a rubber edge as well. I didnt think about that touching but didnt test the system to see if it would rattle. ALSO.

A second 8" is going into the other cubby S well ladies and germs >

 

Great idea, I'm a fan of making use of cavities behind interior panels.
For us 4-door folk, a box like this may fit under front seats. Area is about 13" x 14" x 5"

 

Most 8 " subs, at least my kicker was, 4 1/2" +- deep so it fit great in my box which was 9.71 x 9.71 x 5.71. The hardwood sheet I used was .71" thick.