For long term storage, tire manufacturers recommend relieving some of the weight from the tires OR increasing the inflation by 10%-15%. The idea is to prevent flattening of the tire body from sitting a long time in a compressed condition. As to how important that is to long term health, it's hard to say outside of a lab environment where all factors can be controlled. Factors such as temperatures, freeze/thaw cycles, mosaiture, sun expesoure, etc all have some effect and it's difficult to to say that how they affect a given Rv tire.