square body chevy under seat box

My son daily drives a 86 chevy regular cab full size truck. With subs behind the seat, there is no room for storage. The cab is built with two large humps under the seat for the side saddle gas tanks. I am going to relocate the tank to the back between the frame rails where a blazer tank would go. Then I can recess a box into those humps and put a sub under each seat.

I am not looking to win any contest, just want to have some nice thump for classic rock, and classic country type music. I am thinking about 300w rms and a couple of fosgate prime 10" subs. Since the box will be partially recessed, I cant really down fire unless I completely rethink everything. If I up fire the subs will it sound like crap if they fire right into the seat bottom?

I could make a chamber that goes over the sub that is kind of the reverse of a down fire setup that would direct the sound behind the seat if that makes sense. I think that would be kind of a band pass type setup and I do not know how to design such a deal.

Any thoughts?

Thanks

Lynn