Don't the trailer tires recommend 65 PSI?
I have no idea what % higher or lower you'd want but if it were me....
On the low side, anything below 60 PSI would be helpful. You'd catch a slow leak or blow out very early.
On the high side, probably anything above 75 PSI or so. Do realize that as the outside are and tire heats up, the PSI will increase. Your most accurate readings are in the morning before the tires roll.
Also, to keep things in check, get yourself an infrared temp gun. At fuel and rest stops, check the consistency of tire and brake drum temps. If one is higher than the other three, something is likely wrong with that tire, brake or hub.
2017 Forest River Surveyor 247BHDS...
...Tugged by a 2016 F250 XLT FX4 SuperCrew, Shortbed 6.2L, 4wd, 3.73...
...Joined with a Husky Centerline TS 800-1200lbs WDH