http://www.goodyear.com/rv/tirecare/tire_storage.html says:
STORING YOUR VEHICLE WITHOUT REMOVING THE TIRES
Ideally, a vehicle in storage should be placed on blocks to remove all weight from the tires. If the vehicle cannot be put on blocks, follow these steps for tire protection:
Completely unload the vehicle so that minimum weight will be placed on the tires
Inflate tires to recommended operating pressure plus 25%. Ensure that the rim manufacturer’s inflation capacity is not exceeded
Be sure the storage surface is firm, clean, well drained and reasonably level
Avoid moving the vehicle during extremely cold weather
Move the vehicle at least every three months to prevent ozone cracking in the tire bulge area, as well as “flat-spotting” from the prolonged strain of sidewall and tread deflection
Adjust inflation before putting the vehicle back into service
I had a similar problem with my first 5er, not MS, same tires though. Hadn't followed (didn't know/wasn't told) the above advice. Had 2 tires seperate one day apart. GY replaced all 5 3 year old tires and paid for the minor damage the second tread seperatiion did. On my MS I now tow it around for 20 - 30 miles every 3 months and haven't had any problems.
Sorry about your problem, but maybe this info will help. Oh, yea, GY never asked if the 5er had been stationary or not...