Polk MM1540dvc setup

Hi polk members.
I recently bought the polk MM1540d subwoofer with a kenwood kac-9105d 1800-watt class d mono amplifier capable of running 900 rms @2ohms or 500 rms @4ohms. At this point I'm struggling with putting the sub in a ported or sealed box and not sure if I should run the sub @2ohms or 4. I'm thinking 4 ohms, I've heard the sound quality will be better. I need some help. How big should the sub box be.. Ect. Thanks