cb,
You don't want to buy an off-the-shelf bandpass enclosure because it will be a standard automotive box that won't last in a boat, it will likely be a universal box which isn't a good match with a specific woofer and because most bandpass boxes are like off-the-shelf bass-reflex boxes in that they are tuned for maximum and peak output only. They will hammer but only as an undamped, narrow, single note instrument. Very similar to bass-reflex, the quality can be all over the map depending on the design priorities. A musically accurate bandpass, which can be absolutely outstanding, will have to be designed for the Thiele Small parameters of a specific woofer and the design is seriously complex requiring computer program assistance. Plus, it will be an exercise from a design and execution standpoint to perfectly mate the enclosure and port against the external compartment vent. If you don't have the tolerance for this then its easiest to go with a custom sealed enclosure or perhaps a custom bass-reflex enclosure. In any case you will need to add a vent into the pass-through area.

David
Earmark Marine