Until you have your coach weighed, it's safest to run max sidewall pressure. Running that high, the rig will ride like a Flintstone car. You'll feel every bridge expansion joint.
After having the coach weighed, you can go to the manufacturers web site and look up the pressure for your weight and tires. There will be a table for singles and duals. Try to get a 4 corner weight. If you can only get axle weights, divide by 2 and add 5%.
The biggest danger is under pressure. Running them at max sidewall is rough but safe.