Inside where the skis are kept under the back seat.
Came like that from previous owner...not sure if it's a great place, but works and is handy. Just two small holes in the liner versus drilling into any fiberglass.
I always kept mine under a bow seat. The decal depicts it to be placed under the rear bench seat but I always felt that most likely a fire will occur in the engine compartment area and the bow was the better place to get the extinguisher.