The correct pressure can only be determined by consulting the tire handbook that all tire retailers have. Their book will have a weight v. inflation pressure graph for your size tire based on the weight each tire will carry.
I would not inflate the new tires above about 60 psi before I consult the weight chart. Your new tires should have greater carrying capacity at any given inflation than the rubber rim protectors you replaced. Over inflation will wear the center tread out of your new tires fairly quickly and will reduce trailer braking traction because only the tread centers will be in good contact with the road surface.
As I was writing this I remembered I have an old tire handbook. I dug it out and found this. An LT225/75R16 will carry 1940 lbs @ 50 psi, 2060 lbs. @ 55 psi, and 2190 lbs. @ 60 psi. I don't know how heavy your trailer is but my guess is it carries about 8,000 lbs. on the trailer axles or about 2,000 lbs. per tire.