Reading this thread makes me glad (well kind of) that I wear out, and have to replace my trailer (and truck) tires once a year. It has been a long time since tire age has been an issue for me.
Brian
There is a similar issue with a common size of heavy truck tire. 22" or thereabouts. Used OTR commercially, a trucker can burn through a tire in 6 months. Problem sets in on Class A motorhomes.... not that many years after manufacture, you can have a great looking tire, that falls apart on it's first high speed run..... a wise wrench friend of mine just went through this, on an older Class A he got this year.
Sidewalls on these 22's are a lot thinner than 19.5's - not what you'd expect, and another example of cost-optimization at work....
Rgds, D.