I think you'll hear it better if its in the sides, not under the rear seats facing forward.
Is the Bose a standard sized speaker? Mine came with old Boses that I replaced and I had to have a plastic ring made to get them to fit because of the huge 9" enclosure behind them despite the 3.5" speaker size. As a result, I couldn't install new standard 6.5" speakers without rings.
Make sure they are a standard size so you can easily replace later. Marine stuff doesn't last forever. From my experience, it could be some oddball size.
Top Gun 1992 22 Classic 540hp rebuilt HP500 King Cobra