3 cubes gross 6" aero. itll get down. mine does. sundown wont advertise this but sa-12s like 2-2.5 cubes go model it. you shall see
EDIT a full length psp aero 18" i wanna say is .3 cubes. 4 is kinda larger for one drive tho. sub up port side you can pull off 3 cubes and an aero, id tune 32-36ish. my buddy has and envoy plenty of space.