We did 9 jlw6 12s in the extended cab of a nissan hardbody (96) and it too up so much room the box had to be built so the seat would lean back into it just so i could fit inside to drive... the amps were in the bed 9000watts... and ever since then i care ALOT more about quality of sound than quantity.
It was only fun at shows or when you felt like being an a$$hole.
Im thinking exelon 8s in the yukons doors (to match the sixs and 5 1/4s already there though now and a custom center console with 3 down firing jl 10s.
and keep my 3 12w3s (sealed) in the rear.. all super hidden discreet stuff.. but with a massive sound range.
mashed out.. 9 12w6s 4 8w6s 8 jl 6.5s and 6 6x9s
Edit(just realized the sub box wasnt built yet in this pic.. oh well its 1 of the only 2 pics i have left of it. Taken the same day)