question about speaker location in my I/O

I am looking for some advice. I have a starcraft 190 I/O runabout. I am looking to upgrade the speakers with Polk Momo. The stock boat has two cheapo 5.25" speakers located to the sides of the front passenger/driver seats at about elbow level pointing in to the center of the boat. I will cut these holes larger and replace with 6.5" polks.
I want to add another pair of speakers though. I could add them in the front bow, or I was thinking I would add them in the rear of the cockpit near the back seat. The only problem is that there isn't really a great place to put them. I could put them on the sides of the rear seat, at about elbow level, pointing in.
The other option is I could install them under the rear seat by cutting a hole into the fiberglass/gel coat underseat storage. It would be facing forward at about mid-calf level of the rear passengers. I was thinking of using 6x9's if I chose the latter of the two options. The only concern there is that they would potentially take a beating there because of people inadvertantly kicking them or throwing the coolers, skis, etc into them because they are so low.

Let me know what you all think. Thanks.

Put them in the sides if you can, as you stated they will certainly take some abuse down near the floor/near everyones feet. 6 X 9's are the way to go if you can fit them. I just replaced my cheapo 6.5's with infinity's. I do have the momo 6X9's on the tower though and as long as you dont try to drive 150 watts each though them like me you should be very happy. They like the juice so I hope your not planning on running them from the deck as that would be a lost cause.