Stereo upgrades - need sub/amp advice.

I want to add some bass to my boat's stereo system. I've got a 185 Sea Ray, so it's kind of tight quarters when looking where to incorporate the equipment. I was looking at the Kicker 10's that don't require a box, but was concerned how good they would sound. What combos (sub/amp) is everyone else using. The other thing is how many subs. I want them to hit hard, but not completely overbearing. I appreciate any information. The factory stereo is all clarion, if that even matters when considering a sub.

Thanks to all respondees. This forum has been a god-send for me. Complete novice when it comes to boating.