Make sure all fuel is drained from carbs. Remove plugs and pour about 1/2 oz oil down each cylinder, then turn motor over as few times and replace plugs. Tape up or block off the exhaust ports. Periodically lean the motor on each side to keep parts oiled. Turn the crankshaft at least once every 6 months to keep it free.
Water is your enemy. I would use marine type fogging oil as it is made to inhibit corrosion in the the presence of moisture...and the aerosol can makes it easy to apply. Don't forget to spray in intake and exhaust ports. Direct the nozzle at the valve stems and turn the engine over several times...valves can get sticky in the guides. Cover the engine with plastic and throw a bag or two of dessicant in with it.
