I don't think there there is any suitable way to power an aircondtioner, carry-on or otherwise, on a small sailboat. I think you'd need a generator to do so, which takes up precious space, requires gas on board and creates a carbon monoxide problem. Also, it might inspire piracy if you were to leave your gen-set running to power the AC in a quiet achorage.
That said a carry on AC can make life at the dock much more enjoyable. My boat allows me to place a cheap window unit in the companionway and still have room to squeeze by. I leave it in the dock box if we'll be achoring out or daysailing, but haul it aboard if visiting another place that will afford shore power. It makes a huge difference when sleeping on the boat dockside. I'll often set it up after returning to the dock, then hit the pool to cool myself off while it cools down the boat. If you can adapt a window unit to your boat it is much cheaper, though you'll have to fashion your own handles.
s/v Palmetto Moon
1991 Catalina 36