I had been wanting to add a/c to my Four Winns 258 Vista for a number of years, but did not want the expense & hassle of installing a marine air water cooled system. I had previously tried a cruise-air over the hatch unit that did not perform well and was also very bulky & hard to store. I have just put in a compact "portable air conditioner" that vents out the back thru a dryer type hose. It took the cabin from 89 down to 71 in 20 minutes last weekend under full sun in 101 degree heat at 2 pm. Cost about $300, weight about 50lb., preety quiet. About 25" high by 18 wide by 13" deep. Runs easily with my eu2000 honda gen, along with charger etc. Not sure if I could use the microwave at the same time yet but not an issue for me. I have it vented thru a porthole using the provided hose & "window" kit. The other benefit over marine air is that I can use it on the trailer as we usually get to the boat late at night & overnight in the parking lot. It also vents the condensate out with the exhaust.