I am looking to get a 15"or 18" to go into a sealed box for sq. Leaning towards the 15" at the moment. Car: 98 Mustang Location: Trunk Amp: MTX te1501d (birthsheet @ 1 ohm is 1556 rms @ 13.8 volts) Wires: 0 gauge on big 3, main battery to second battery in trunk, & from second battery to sub amp. 4 gauge to highs/mid amp from second battery. Stock 130a alt. but I'm getting a 270 Mechman and xs 3100d( will be under rear seat) when i order the sub or shortly after. If i go with the 15 the box will be 26.5L x 26.5D x 11H about 3.5 cubes before displacement. Sub will be upward firing. I'm tossing up the idea of the 18" but don't have experience with 18's. Any idea's if the 18 would be with the trouble? Thanks in advance Also the reason for upgrade is because my 12" mtx thunder 9500 @2 ohm just isn't enough anymore