Yes you could...but in a celica the area is too small to even cross over anythign and you wouldn't get the imaging of the sub anyways
imaging? imaging is for front stage. a sub bass frequency is non directional. the wavelength of a subwoofer at 50hz is the same no matter the driver size, be it 10" or 18". it would be better if you stayed the same size driver though. if you are going to do the well as you diagram it would be better to do 3 10's. no i know MTX had a demo vehicle that had 2 12" woofers and 2 15" woofers. but when using different size drivers, you must use different amplifiers, and cut them off at different frequencies. ie set the 10's for like 250hz and the 12 at around 80hz. if you did not do that then the bass would be muddy as hell, and overpowering. also, when using multiple woofers, use the same box design, ie dont use the 10s in a sealed box while using the 12 in a ported. that would fuck it all up. i have heard 3JL8's that i swore was a 15 it was in a surburban. but also with all this bass you want, make sure you improve the midbass also. get some really good 6.5 midbass drivers.