i had a 48" long box in my 95 regular cab, and it was large enough for 4 10’s, fitting 2 12" subs would have required either seat mods, or cab mods
i had 2 subs in the box, each out towards the end, then stacked 2 narrow subs between the seat backs, lower amp mounted totaly to the box, upper amp mounted to the box and to the rear sheetmetal , and then i had a few more amps and crossovers mounted to the rear wall above the box . behind the seats
everything was tuned by an old friend who used to do competitions, and it sounded fucking amazing, and it rattled the entire shop @ schmitts teh day he finished tuning it. i had something like 600 watts going thru the subs alone
but i also had everything covered in sound deadening … rear wall, floor, door skins, firewall, roof, and anyplace i couldnt lay sheets, i sprayed undercoating. i also spent time tracking down rattles
i had plenty of compliments on the system, alot of which were from strangers so it definantly sounded good enough to be worth the effort