What is your definition of "long term"? Axle manufacturers (Dexter) recommend supporting the wheels off the ground when sitting for months. This is to allow rotating the wheels periodically to keep the bearings coated with grease; otherwise the grease migrates slowly to the bottom, allowing the top-side roller bearings to rust. Tire manufacturers recommend the same practice, to avoid "sidewall fatigue" in one spot. They also recommend inflating to 10psi over sidewall maximum if you leave weight on the tires. If a tire develops sidewall cracks while sitting, they are almost always in the sidewall bulge first.
I agree that something should be used to avoid contact with earth if you leave weight on your tires.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"