maybe
you can get away with a single outlet the main cabin if you don't spend nights on your boat. There are only going to be a handful of night that you will need a/c in the sleeping areas of your boat based on size and temperatures at night vs day time temps and you can always use a fan to circulate the cold air on those nights if you need it (I am assuming you know you will need to be at the dock or have a generator to run this). That being said the factory would have put in three, a vent in the v berth, the aft berth and the main cabin. If it was me I would have three. My question is why don't you install this yourself? these units are "plug and play" on the wiring side and not that hard to install. Lots of good info in archives on installing and venting. Some good articles about using an existing thru hull vs. installing a new one. This would make a good winter project. Cash and carry you can buy a 12k BTU unit and all needed vents and accessories to install for less then $2000 (check out Defenders catalog or web site). So that leaves the $3800 quoted for installation. Not a bad weeks pay cuz it will take you a good 40 hour to do it all but unless you make more then that take home you will still be ahead of the game. On a one to ten scale ten being mechanically inclined at 6 or 7 should be able to install, and the factory will give you free advise if needed. May I suggest that you can start out with one vent only and add as you see fit and to also get a unit that will reverse cycle for heat as well as cool you will be surprised how much you will use it or how much more you will/can use your boat with both a/c and heat. Good Luck !