For OE tires the correct tire pressure can be found on the certification label, tire placard or in the owner’s manual. With ST tires it’s going to be the same as the maximum amount found on the tire’s sidewall.
ST tires are designed to be operated at full sidewall pressure - all the time.
Weighing your trailer and finding out what each tire is carrying is very helpful in finding out if the trailer’s overloaded. From the weight findings you can move things around and balance your load. Or remove some stuff if overloaded.
Remember, tires on RV trailers - all of them - are fitted to the vehicle’s GAWR.
Using less pressure than the vehicle manufacturer’s recommended pressures is unsafe and unwise.
Now, for the OP. Are your new Maxxis tires the same size as the OE tires? Are they larger with more load capacity.
Maxxis is one of the few ST manufacturers that supports the use of their load inflation chart. I recently had a phonecon with one of their area reps. He would not provide a recommendation. He said that is the responsibility of the vehicle manufacturer or tire installer when replacing OE tires with tires larger in size or increased load capacities.
The air pressure needed to provide the load capacity of the OE tires would become the new recommended pressure (RMA).
TireHobby