jbl gto804 8 subwoofers

hey was just wondering if anyone has had any experience with these 8" subwoofers.  Was thinking about putting 2 of them in a ported box in a four winns 195 sundowner in the cuddy cabin and just wondered if these would provide descent bass or if I need to go with like a single 12 or 15 in a ported box.  just thought that being the 8s would require a lot smaller box I would have a lot more room since a comparable single 15 requires like a 3.5 cu ft ported box.  Plus I am going more for sound quality rather than needing to be heard halfway across the lake.

Also If you comment I was wondering if you could give me any imput on jbl subs and amps whether they are descent or if the amps are underated for power and just things like that.  I am really thinking of jbl since they don't seem to require an ungodly amount of power.

Thanks