2011 Sunsport 242 Stereo upgrade help

I have a few questions for you stereo guys who may have worked on the 242s.

First of all I have the factory system with the kicker 6.5s everywhere, the Roswell light/speaker bar, and 12" kicker sub. Of course the sub is not build into an enclosure, but just into the cockpit kickboard, free air into the front seating area.

The stereo sounds very mediocre, is underpowered, and I'd like some upgraded sound. Not looking to be the loudest on the lake or anything like that. I eventually go with a couple sound projecting speakers on the towers, but that's for a later date on down the road.

The sub is quite pathetic to me (I'm sure due mostly to the factory just slapping it on the kick panel with no enclosure). I have some components that I got some killer deals on, and I plan on trying to use them if at all possible.

Here is what I have: I know it's not JL or Wetsounds, but I don't want to spend that kind of coin at this point, and like I said... I got this stuff brand new and super cheap.

I have 2X POLK DXI 12" DVC subs
I have 2X Kicker DX400.4 amps (car audio)

The amps are 4X50 @4ohm and 4X100 @2ohm.

First thing is, can I (edit someone) build an enclosure which will allow me to run the 2 12"s above in a sort of diagonal arrangement on the kickpanel. I know it is tight, but I think it should be able to be done. Any input here?

Next... I have decided I want to replace all of the factory 6.5 kicker coax speakers with Polk mm651UM 6.5s.

Does anyone know if I can install these Polk 6.5s in the Roswell cans on the light bar as well?

Also, if everything above sounds like it will work... do you think replacing and or adding to the factory amps with the 2 kicker amps above will do the trick to power the polk subs and the polk coax speakers throughout the boat?

I am also probably going to add a third battery to the existing two.

Any suggestions recommendations would be greatly appreciated.