andi have a kicker kx1200.1 and two 2006 12" solo baric L7s ready to be installed.
i called my local stereo shop 2day and he said that you cant fit solo baric l7s in the back of a ext cab truck, but he said he has the same truck with 2 comp VR 12s and they kick hard and fit fine.
in my catalog it says the 2006 l7s mounting depth is 6-11/16 and the comps are 6-3/16.
would half an inch really make that much of a difference where its impossible to get it under the seat without taking out the backseat?
i have a 98 ext cab sliverado...and i'll tell ya, you will have a hard time getting a comp VR fit under the back seat. there is literaly no room under the back seat.
most down fire boxes i see for mid 90's silverados only have a max mouting depth of ~6". you may be able to modify a prebuilt box and get it CVR's in...but you wouldnt have any room for the poll vent to breath.
one other thing...since there is very little air space under the seat, IMO you wouldnt have nearly enough airspace for L7's. (the max you can even get out of that area is ~1.6cuft, before sub displacement)
truth be told...you would need a shallow mount sub that performs well in small inclosures. (.5-.7cuft...i.e...10's)