i have been thinking of a cheap way to get some air conditioning on my boat at the mooring also. i am not sure of loads and how much the generator can take but was considering one the the 2000wt generators from honda and one of the 5000 btu portable a/c units found at walmart or similar stores. they vent out through a hose which you can stick out a hatch. cost i have seen 300-400 dollars. plus you have to buy the honda generator. some places list the info on how much energy they use but i am not sure how that equasion goes.
i assume the startup and running wattage would have to be less than 2000 watts. (if using a 2000watt generator)