Locations:
Right now I have one B-Iin trunk cabin and one B-II in the helm cabin. I may add a larger combo ABC-rated extinguisher in the cockpit up under the rail/washboards.
Other:
Like those links state, I tip them upside-down every month or so and give them a sharp rap on the bottom to make sure the dry powder hasn't settled into a solid cake. During the Winter layover, I store them upside-down.
Having them is key ... maintaining them properly is critical!