If I understand right , your trailer weighs at most 1000 lbs loaded and all.
Googled your tires and they are loadindex 121 S wich means one tire can bare a piece, 3200 lbs AT most likely only 35 psi.
This AT-pressure is the only thing I dont know for shure, but going by the sises I think its yust standard load, and no XL/reinforced/Extraload, and no LT tire.
But look on sidewall for that , search for something like AT 35 psi or maximum cold pressure 44 to 50 psi , then its a Standard load with that AT-pressure of 35 psi, or in case of European system 36 psi.
Then you can drive up to 160km/99m/h with that weight on it without overheating the tires.
You dont need that , you can do with much less.
For on the road I am able to calculate it for you as "pigheaded Dutch Selfdeclared Tirepressure-specialist"
Filled it in my motorhome calculator in wich I use a reserve of even 18 % and use my determined formula that is even saver then the European formula.
Filled in 1000 lbs with that 18% reserve and lowered the loadindex by 8 to 113 to give it lesser deflection, because your tires have large profile blocks that cover a part of sidewall , so lesser sidewall is left to flex.
So did everything to give the highest pressure .
Then came to 1.2 bar/17 psi , yes that low and then all the reserves and pessimistic calculation.
so you dont need higher pressure for driving even 160km/99m/h on the road.
You sertainly wont drive that speed I think, but this pressure , to my conclusions will still give no discomfort ( for the things that means it wont shutter that apart or trailer goes dancing).
for off road tiremakers give lists and go for on track at that low weight from 80% of the pressure for 65km/35m?/h on the road. For in Sand/Mud even 50% of the pressure needed for 20km/12.5m/h on the road.
Still busy figuring out what system the tiremakers use for that , but estimate you can even do with even 0,6 bar/9 psi on track.
But check if I am right about the tires 35 AT pressure , give everything you find on sidewall that can help met with that.
EDIT: Searched better for your tires, and found LI 112 and Li 115 so think those are Standard load and XL, and you then must have C-load /LRC with AT pressure of 50 psi . Asumed American system because comparable Eur 6 plyrated is AT 55 psi, so can be wrong there still. Would mean 10% higher pressure calculated.
This would mean for on road up to 160km/99m/h with same carefull extra's and calculation 1.7 bar/24 psi. So probably for track about 16 psi and in sand/mud not higher then 9 psi.
