Maybe one 12" L7 if you use all of the availible space? Like under the seats, using the center consol(if you have one?) all of the space behind the seats.
one of my friends has 2 12" l7's in an 91 silverado regular cab an he has them behind hi sseats in about an 4 cube ft box an each sub gettin about 2 cb ft an he has an 1400 w mmatts amp its hits really hard but he paid 800 for the amp an 750 for the subs an here i am with my 2 12" ed o.14s and a jbl1200.1 that i paid 700 for my whole system an mine hits almost as hard as his although i no his woul dhit harder in a bigger box an u wanna no whats bad is he pai some shop 150 dollars to build th ebox an 200 dollars to install it he got ripped a new @$$