you'll have to find a spot for the amp. take the time to screw it in place, loom the wires, and route it well and logically. you want the amp out of the way so you can easily move/rotate/flip the box. hopefully the wires you have are long enough to do that.
when you face it forward, you'll have to make filler panels for the sides and top. that box is blocking a lot of airflow to the cabin. facing them backwards you are going to lose a lot of bass out of the car, that will never make it to your headrests.