Well all this stuff has been covered over the years. Here is what I remember..
Tires, covering is good - keep them out of the sun, most of the "protectants" tend to make it worse - they look good, but draw out the oils sooner and in the long run tend to increase cracking. Driving the bus occasionally is best, flexes the sidewalls and distributes the oils.
Batteries - keep a trickle charger of some sort on them all, and of course keep them filled with distilled water. Its charging too fast that can boil out fluids / gases.
Probably best to drive it once a month for 100 miles ( lets see thats how many gallons at todays's prices?) Driving is way better than just idling it. In fact, idling, even a fast idle may be harmful especially to two strokes. The engine can't get hot enough unless it's under load. It needs the heat to burn off water, impurities, and keep fuel from building up in the slobbert tubes. And idling does not do anything for the rest of the drivetrain and wheels etc.
I end up taking mine out at least once every 3 months during spring and fall, every month during the winter and for a month during the summer.