We have a 'central' AC system which I installed on W42.
Second summer running.
18500 BTU.
Opted for heating coil. Works well also.
Cools well on 90 + days. Heats well to 40 F days.
Mfg Flagship Marine.
Biggest challenge was running 4" duct work, drilling 4 1/8" holes, etc.
Downside to AC is added blower noise. Blower and minor compressor water pump noise/vibration also present.
Did my install in the early spring of 2012.
Best,
Tom