One of my projects for this winter was upgrading the factory 6-speaker in-boat Kenwood system in my Supra 20SSV. My goal was to add a Sub and Tower speakers and do it under a $1000 budget that I set for myself. I basically knew nothing about audio systems and got most of my info from this forum.
I built a custom sub box out of MDF, coated it in "Bed-Liner" and wrapped it in SC carpet. I only lost about 3 inches of foot room and the sealed box is about 1.4 cu. ft. with a 12" Kicker Sub.
The amp is a Kicker IX 500.4 2 channels bridged running the sub and the other two running the tower speakers.
Thanks to Earmark Marine, I picked up a pair of Exile SXT65Q on close out.
It's not like many of the amazing systems I see on this forum but I am very happy with the results and it is something I can build on next winter.