Whether you use a ported or sealed box depends on what kind of sound, and sound volume, you're looking for. If you want tight, accurate bass, a sealed box is excellent [and simple, and cheap, since you already have the right box for the driver], but it'll require a lot more power to get the same volume as a ported box. A ported box is less accurate, and "boomier," but will be much more efficient [louder per watt] than a sealed box. [Not all subs are meant to do both, but yours is.] Free air mounting is possible with some subwoofers, but the one you have is designed to work in an enclosure, and the one you have is just fine for it.
Whether ported or sealed, you're going to need a separate amplifier for the subwoofer: low power is more likely to do damage to the sub than high power, plus it's going to sound pretty awful, as you've noted. I'd recommend something in the vicinity of 200 watts for that particular sub. Keep in mind you have a dual voice coil sub, and hooking it up wrong can damage the amplifier it's plugged into - or, in your case, the head unit it's plugged into. If you're not familiar with how to wire a dual voice coil sub, don't hesitate to shout out.
