Looking at the specs of the trailer the GVWR is 8500lbs, which means the TAW will range from 7225 - 7650 at GVWR with 10-15% TW.
That's just based on operating at GVWR.
7650 is 1912/tire. If you round up to 2000/tire for a little wiggle room them you only need ((2000/2540)*65) 51 psi per tire. 55 psi is plenty of air and you won't have damaged them from that pressure.
If you are doing short trips at speed of 55-60 then 55 psi is plenty, but for extended freeway trips at 60-65 then 65 psi would be better.
Again, hitting the scales is the best answer.