Have used a Cruisair unit to sit on the cabin top hatch and it worked very well. Coincidentally used the unit on a 14 day trip in an h34 from the Cheaspeake Bay to the Long Island Sound and back in the middle of the summer. I have used built in units, window units, portable units. and watercooled unit which came in a Samsonite suitcase. The window units worked well to sleep, but blocked the companionway and pooled condensation in the cockpit. Tried setting up a window unit on the top hatch with a baffle to separate the intake from the output but could not entirely avoid recirculation of the cold air to prematurely cycle the compressor off. The Samsonite suitcase unit worked fairly well but was noisy and cumbersome to set up the water cooling hose. The portable units expel a significant volume of compressor cooling hot air creating a negative pressure in the cabin which brings in hot and humid air from the outside to replace it plus the exhaust hose radiates heat. (not very efficient in a boat environment). The built in units work the best but are usually larger requiring shore power to operate. The Cruisair has an advantage as it can be easilly operated by a portable generator. The one we used was the 5,000 or 6,000 BTU model.
