I was checking around for some basic information on how to determine the age of tires. So in my research I came across this article below which is well worth the time it takes to read it. I usually promote blocking up your rig so as to reduce the sidewall load and risk of fracturing the sidewalls when sitting for extended periods of time. This article coincides with my thoughts on sidewall failure from various other sources.
It also supports my belief that the shiny tire thing coatings may be reducing the life or your tires and putting you at risk.
Please read this article and you will hear it from people who manufacture tires and not just my opinion on the subject. RV Tire Care