Bill,

The Lycoming answer guys at OSH told me the best long term preservative procedure is to fill the engine completely with oil.  Cap off the exhaust ports and fill with whatever oil is on sale at your local auto parts store.  Tilt the engine at all angles to get the bubbles out.  Then remove the sparkplugs and fill each cylinder if not already full.  By displacing air in the engine, corrosion can’t start.

Steve Colwell