I suspect Florida is very high humidity. Turning the engine over a little once a month by hand should help. Some oil in the bores should not really hurt either.

Just make sure to turn the engine over with the starter with the glow plugs out to blow any oil out that might have remained up there. That is just before the engines go back into service.

The glow plugs can be left finger tight to enable adding a little more oil from time to time. I would seal the intake and exhaust as well. This way you are pretty certain things will be as you left them with little effort.

Overkill perhaps I realise as well. Better safe than sorry also comes to mind. The true length of storage of those engines is possibly going to be far longer than what is thought at this time.