I used to be "in to" car audio many years ago. I have seen boxes built underneath floors. Welded boxes lined with MDF, sound deadening matt, fiberglass, whatever. Not sure how well it sounded, but the idea was to save space and get points at shows. Anyway......
I have a 10 in my 98 reg cab. I put deadening matt on the back wall and then used MDF on the other sides. I messed up the face and made it a smidge too long. I didn't realize I was F'd until it was glued in place with liquid nails. I used spray foam to seal the gaps. Just cut/sanded it all smooth. I used the factory carpet from the back wall to cover the face. I then painted the grill tan. The sub is mounted low in the box so even with the armrest down it's not super easy to see. Since I know where I messed up, I am thinking a smashing it out and trying again. The good thing is that I think I only lost maybe an inch or so of leg room. The amp is mounted behind the passenger seat. I move the jack behind the driver side. It just stands up and it boxed in by the sub box, back wall, side wall, and the seat. I need to find a better way to do it. Just need time......and a friggin Torx wrench(?) to get the seat out. The box goes from plastic panel to panel in the back. I really want to cut these, but don't have replacement ones if we ever sell the truck. Then again, it the box is sealed to the truck......what does it matter?
As soon as I figure out how to post pic's, I will do so. Do I have to put them on my photobucket account then here? Why can't we just cut/paste?
edit: well I think I figured out ..... something. I used the "advanced" button. Anyone know how to just put the pic in instead of those attachment's?