Help pick cheap subs for our pontoon boat...

[MLA]

After rereading your posts, I do not see mentioned whether you are thinking sealed or ported enclosure. Most subs either lean one way or the other, with a few falling in the middle. I would decide on the enclosure type, then go with the sub that is best suited for that enclosure type. The enclosure location will come into play now. The boat may dictate to some degree, which way you can go.

[EarmarkMarine]

Just trying to offer Eric some application advice, independent of brand, before he puts forth all the effort and makes a mistake. Mike is right in that the brand is irrelevant if the execution is poor.
I've also been to plenty of open/outdoor concerts, with elevated stages, and no amphitheater, and the bass was awful away from the stage regardless of the number of woofer cabinets.....despite the best efforts of the sound engineers. They can only take what the venue gives them. And that scenario actually has benefits that a pontoon would never have.
If you are placing four subs overhead for the sole benefit of those on the upper deck or on the lower deck it would be passable, but if your expectations are to generate bass away from the pontoon you are going to be sorely disappointed proceeding this way.

David