lot of work, but I found this document a few weeks back, and it talks about proper storage, and one of the issues was long term storage.
Discount Tire Trailer Tire Facts
Trailer Tire Applications
•Trailer tires are designed for use on trailer axle positions only. They are not built to handle the loads applied to, or the traction required by, drive or steering axles.
•Always inflate trailer tires to the maximum inflation indicated on the sidewall.
•Check inflation when the tires are cool and have not been exposed to the sun.
•If the tires are hot to the touch from operation, add three psi to the max inflation.
•Underinflation is the number one cause of trailer tire failure.
Load Carrying Capacity
•All tires must be identical in size for the tires to properly manage the weight of the trailer.
•The combined capacity of the tires must equal or exceed the Gross Vehicle Weight (GVW) of the axle.
•The combined capacity of all of the tires should exceed the loaded trailer weight by 20 percent.
•If the actual weight is not available, use the trailer GVW. If a tire fails on a tandem axle trailer, you should replace both tires on that side. The remaining tire is likely to have been subjected to excessive loading.
•If the tires are replaced with tires of larger diameter, the tongue height may need to be adjusted to maintain proper weight distribution.
•All "ST" tires have a maximum speed rating of 65 mph.
•As heat builds up, the tire's structure starts to disintegrate and weaken.
•The load carrying capacity gradually decreases as the heat and stresses generated by higher speed increases.
•Time and the elements weaken a trailer tire.
•In approximately three years, roughly one-third of the tire's strength is gone.
•Three to five years is the projected life of a normal trailer tire.
•It is suggested that trailer tires be replaced after three to four years of service regardless of tread depth or tire appearance.
•Trailer tires are not designed to wear out.
•The life of a trailer tire is limited by time and duty cycles.
•The mileage expectation of a trailer tire is 5,000 to 12,000 miles.
Why Use An "ST" Tire
•"ST" tires feature materials and construction to meet the higher load requirements and demands of trailering.
•The polyester cords are bigger than they would be for a comparable "P" or "LT" tire.
•The steel cords have a larger diameter and greater tensile strength to meet the additional load requirements.
•"ST" tire rubber compounds contain more chemicals to resist weather and ozone cracking.
•The ideal storage for trailer tires is in a cool, dark garage at maximum inflation.
•Use tire covers to protect the tires from direct sunlight.
•Use thin plywood sections between the tire and the pavement.
•For long term storage, put the trailer on blocks to take the weight off the tires. Then lower the air pressure and cover the tires to protect them from direct sunlight.
•Clean the tires using mild soap and water.
•Do not use tire-care products containing alcohol or petroleum distillates.
•Inspect the tires for any cuts, snags, bulges or punctures.
•Check the inflation before towing and again before the return trip.
Keys to Avoiding Trouble
•Make sure your rig is equipped with the proper tires.
•Maintain the tires meticulously.
•Replace trailer tires every three to five years, whether they look like they're worn out or not.
Trailer Tire Warranty
•The Carlisle trailer tire warranty applies to the original purchaser for three years from the date of purchase or until the tread depth reaches 3/32".
•The OE (original equipment) warranty goes into effect at the time of the trailer purchase