Hey guys i know that having super/ext. cab can be a pain to put a sub box in, but i have funally solved my problem. I went to the local welding store bought 2x2" square tubing and cut it into peices about 2.5inches long. I then drilled holes in these and bought longer bolts (12mmX100 mm) and used these to hold the seats to the floor. it looks like this
this is the middle one -
this is the one behind the back of the seat in the middle
and these are the front edges
ok so now this solves the problem that the seats are to shallow (cant hold a sub underneath) then i built this box. I kept it out of the way of the jack, and could've built it for more storage space but i have a tool box for that i just keep my tow strap and some paper towels (fastfood at work). but it is nice i can put up dimensions later if you want. this is what the box looks like.
the sub is a 10 inch but it could be made to hold a 12(just make everything bigger) but the storage is actually pretty big. The sub sits about mid way underneath the bigger seat.
Hope this helps some of the ext. cab people because i know i to hell and back to find a way to get to work. and sorry for crappy pics they were cellphone pics.