How long are you storing it? I hate to see a freshly machined and assembled motor just sitting around.

I like the desiccant that John pointed out. Wonder if they make something like that for in the motor, like maybe through the distributor opening. I use DampRid (desiccant) in the engine compartment of my boats when storing for winter. It works.

I think fogging oil is normally used when the motor is running but probably through the plug holes would be good too. .

WD 40 is more like a solvent than a oil. I'd consider something else for longer term storage.