This year we plan on keeping LUNASEA on the north shore for the winter, is there anything special that needs to be done. What else do I need to do?
If the boat is to be kept in the water, unless the water can freeze hard, there's no need to winterize any systems or equipment below the waterline because boat hulls take their temperature off the water temperature and equipment and plumbing entirely below the waterline can't get any colder than the hull. However, unless you're planning to use the boat regularly all winter, there are systems that do need to be prepared for extended layup...starting with the sanitation system:
Pump out and THOROUGHLY rinse out the holding tank. You don't have to fill the tank to do this...put a few gallons of water into it via the deck pumpout fitting--'cuz that sends the water into the tank at the bottom to stir up any sludge and hold it suspension so it can be pumped out...pump that out. Repeat...repeat...repeat...until you're pumping out clean water.
Follow mfr's instructions for preparing any treatment device (Lectra/San, ElectroScan, PuraSan) for extended layup.
If the toilet is above waterline, it should be winterized. First flush enough to clear ALL the water out of it. If a sea water toilet, remove the flush water inlet hose from the thru-hull (close the seacock first!), stick it into a jug of non-toxic potable antifreeze and flush the toilet to pump it all through the system all the way into the tank. Even if the toilet is below waterline, if any of the bowl is above, it needs protection and just pouring antifreeze down the toilet won't provide any.
As for the fresh water systems, whether the water tank should be left full or empty has supporters in both camps. If plumbing is above waterline, there should be no water left in any of the lines. Draining the plumbing may require installing some quick connect fittings.
As for all other systems, follow mfr's instructions for preparing for extended layup. If you don't have 'em, you should be able to find owners manuals on the net...if a system is too old for it to still be available, contact the mfr directly.