Mike,
I know it's been almost a year since you posted the question. I own a Monticello 2004; and also keep it in dry storage. I've been running the AC with a Honda EU2000 with great results. My ac's water pump has always primed after some cruising; (water forced through the sea water **** into the pump). Make sure that the seawater **** valve is OPEN in my case it's a yellow lever on the bilge's port side . If that doesn't work, the raw water filter is between the fuel tank and the engine right in front of the bilge pump (in my case) if you unscrew the clear cover of the filter (don't have to remove it) water pressure will start filling the round container. Once full, tighten the nut back up and voila; you should have the system primed.