As far as I know it applies to all tyres for all applications. While UV may speed up the process the tyre ages from the day it is made. Once past 6 years or so then it's life expired. An eagle eyed MoT inspector may pick it up, even if it looks like the tyre is in good condition.Having read about trailer tyres having a shorter life, it seems it’s the sunlight (UV?) that causes the degradation, hence storage before sale is ok. Trailers or caravans presumably just sit in the light day after day.