maxxis tire storage The most common condition is sidewall weathering cracks (multiple cracks along the flex area of the sidewall), usually related to long term inactivity, direct exposure to UV rays, direct exposure to high levels of ozone, or exposure to alcohol or petroleum-based cleaners.
And of course read what Maxxis says about tire storage in the clicky.
Goodyear says this about RV tire storage.
Goodyear rv tire storageHow Not to Store Your Tires
Don't store tires in an area that is wet, oily or greasy
Don't store tires where they are subjected to direct sunlight or extreme temperatures
Don't store tires near electric motors or other ozone-generating sources
Don't store tires on black asphalt or other heat-absorbent surfaces
Don't store tires on or adjacent to highly reflective surfaces such as sand or snow
Sitting in direct sun/storing on wet ground or in water for months at a time over several years I've found can cause checking on even a LT tire on my equipment trailers.