re speakers in the galley, sound quality from those speakers will be better if those speakers are in an enclosure/box, and the storage shelves in the cabin do not qualify as "enclosures" from an audio standpoint. My galley speakers (no enclosure inside the cabin cabinet) sound good, but would sound better if they were inside their own bozes.
Of course, you won't really get to turn the stereo up all that loud to hear the difference, so...
(at least in the campgrounds)
there are advantages and disadvantages to both installed versus mobile speakers. The only real disadvantage to installed (other than cost) is that the stereo/head-unit drains the TD battery, and it costs money to install.
I used speakers that were designed to be used IN a sauna. They are supposed to be more "robust" than speakers designed for autos and boats, but I am sure an auto or marine speaker would be fine, though perhaps not as high quality from a sound standpoint. I got a really good deal on the speakers, so I jumped at it.
Go small small small. You do not want to lose any inches of shelf space in the galley or in the cabin.
Portable speakers really isn't a bad way to go, though you do have to find a place to "store" the iPod dock, which can be a PITA. But it would be nice to carry the dock over to the picnic table and listen to some tunes, on occasion. Of course, you can still do this even if you install speakers.
-Al