If this is the boat you are going to keep for years to come, spend the $1,500 and put in a proper marine unit. About 10 years ago, I installed a 12K BTU MarineAire unit on Paloma. Pulled the water from a T-pipe I put on the engine water inlet, put the pump under the starboard couch and the unit in the hanging locker with vents blowing into the V-berth and the main salon. What a difference, from the window unit I had in the companioway. Even on the Gulf Coast on a 100 degree day and 100% humidity, whithin an hour, you have to move the thermostat down to about 50%. I also have padded hatch and companionway covers. - they help keep the heat out as well.
s/v Paloma, Bristol 29.9, #141
Slipped in Bahia Marina, easy access to Corpus Christi Bay and the Gulf of Mexico.