Sealed Sub Qtc

I have a JL Audio 13w3v3-4 sub that I am going to place into a direct radiating sealed enclosure under the helm. It will be powered by a JL Audio 500/1 amp. My primary desire for the sub is to reproduce the bottom octaves accurately and musically. Much of my music contains acoustic instruments and unprocessed vocals, so I'd like it to sound, "natural". Moreover, we listen while floating around at full stop, never while under way.
The JL literature recommends 1.5 cu ft net internal volume which produces a Qtc of 0.89 and F3 of 40.4 Hz. This would create a small increase in output in the upper bass range of the frequency response.
The consensus on internet boat forums seems to recommend Qtc of 0.8. My calculations say 2.012 cu ft net internal volume produces a Qtc 0.8 and F3 of 39.04 Hz. This would play slightly deeper and roll off more smoothly.
Because of space constraints, I would prefer to build the smaller enclosure, but I don't want the upper bass emphasized.
I have some experience building and installing subs in home audio and autos, but none in boats. I know there is little if any cabin gain in a boat. So, I'm looking for input, advice and anecdotes for this installation.
Some thoughts I had about using the smaller enclosure:
Could I go with the smaller enclosure and EQ out any upper bass humps?
Maybe add fiberfill to the enclosure to get that phantom 5-6% volume increase?

Any thoughts are appreciated.

In my experience with JL Audio, they are going for a balanced and neutral sound. I think listening tests by some very critical ears are the final determination and that is why you see some small deviation in the target system 'Q'.
Too low of a Qtc sounds deep but a little dead. This is a large and low resonance speaker with lots of low end reach. I'd trust their recommendation. Then add polyester polyfill to test what a lower 'Q' will sound like.