When the RV trailer is required to set in one place for extended periods, the owner should try and to reposition (rotate) the tires 180 degrees every 90 days - or more often - if possible. Tire manufacturers use a lot of chemicals to help prevent ozone damage, aging and weather checking - just to name a few. Over long periods of time those chemicals will migrate to the bottom of the tire leaving all areas above them unprotected. Our cars, trucks, etc. are not normally idle for long periods and do not suffer from the lack of protection.
Another beneficial safety precaution would be to provide a barrier between the surface the tire is parked on and the tire. Over long periods of inactivity water can permeate into the tire treads and decay them along with the tires innerliner and maybe even the carcass.
FastEagle