Busa is so right - tire pressure is CRITICAL to tire survival.
I do not try and out-guess the engineers. With only one qualification - here in the mountain and desert west, in the summer we face extremes of temps. You folks in the east think 90 degrees is hot. On the deserts I have to cross, 110 or more air temp. is not unusual - resulting in pretty seriously hot pavement temps. Couple that with heavy loads, and you have hot tire carcass temps. Air expands when heated. I find if I start out in the cool of a morning at, say 10 lbs psi under the recommended temp, by noon I am up to or even slightly above the correct pressure.
Additionally, the big problem I see with trailer tires is that most people store their trailers outdoors, where temperature/sun damage issues hasten the "drying out" process, coupled with the fact that even under ideal storage conditions, chemical changes means we are stuck - we HAVE to, if we are interested in highway safety, replace tires after an interval - I personally would say even under ideal conditions, ten years should be a maximum.