It doesn't matter what position their stored in or whether you leave the tires on or not, tires will rot eventually regardless if on or off the rim. I have set of tubular rims that went from leaning against a wall for about 15 years to hanging for another 14 or so years, so their 30 years old about and the hubs are fine and the wheel is still true., there is some minor oxidation around the spoke holes, maybe if I had stored them in thick plastic bags the oxidation may not have occurred?
Tires? Well I bought 2 bikes that were over 20 years old and both had their original tires, one set sidewalls had completely cracked and was unsafe to ride but like an idiot I did anyway and one blew right out; the other bike tires sidewalls were fine, like new! I heard if storing tires to keep them away from electric motors.