M, you mentioned the number of miles on the tires but neglected to tell us the age and pressure you typically run
trailer tires(commonly marked w/ "ST" in the size stamp) have a 5 year maximum life expectancy
going past 5 is not to our advantage any more
there is a DATE STAMP on most tires today which is 4 numbers in an oval(usually) ring

- 31384217_10156272631584257_7175265691181651354_n.jpg (191.56 KiB) Viewed 2162 times
here is a better pic(not a dirty old tire

- dot_age_tire.jpg (69.06 KiB) Viewed 2162 times
using the date stamp in the 1st pic you can see that tire was made in July(30th week) of 2007('07)
check the age of your tires and when they hit their 5th birthday replace them
aso ALWAYS run MAX RECOMMENDED PRESSURE which shoud be in the 60psi range for the tire you showed us
runnung max pressure makes the tires run cooler
either issue and most certainly both together could be your culprit
HOWSUMEVER in this day n age the products on the market don't measure up with the quality i grew up with
YOU ARE RIGHT
KEEP AN EYE ON YOUR TIRES(TRAILER & VEHICLE
sw