i800collect knows alot about this stuff. he can correct me if i say something false lol.pros for in trunk: easier to get more output from subs, way more choices, you can move the box around if it doesnt sound quite right. obvious con is less trunk space and some added rear weight. pros for free air is cons for the box setup. you dont have to make or buy a box. cons: less to choose from, less output than a boxed sub, hard to tune to a certain frequency.