I have a 2011 XB so let me fill you in on what you have to work with.
1. If you use a 2500 you will be fine, if not find 3k worth of cheap amps for burps. Like 2 of the apsm-1500s strapped $240 total (just dont expect to pound on them every day with the same results as a sundown amp) Any higher you wont have the electrical to back it without quite a bit more $$$$.... Even on that 2500 u need a couple of bats fully charged per burp because those alts **** even if they are 110 amps.
2. On this lower power cone area is your friend. You cant wall it because those guys with walls will blow you out of the water. What you can do is seatline down or headrest down. If you stay below the seat line/window line you have about 4 cubs - 5 cubs (if you use the space over the wheel wells and the angle behind your seat. You have quite a bit of room below your floor so remove your floor and use some of that space for bats, amps, or even more box. You can do a pair of 12s to the rear or 15's up. Personally I would go to the head rest line with 2 aq hdc3 15's on 3k rms firing port and sup up in an 8 cub box which is everything you have. Tune it high in the mid 40's and let it rip.