Max pressure is 100 psi. Anything under that is acceptable. An empty vehicle would need only 10 psi. Add air for heavy loads, towing trailer, car, etc. Increasing pressure can be helpful if driving in a strong crosswind to minimize sideways push when trucks pass, etc. Also look at how the coach sits when loaded. Rear end should be level or just slightly higher than front. Adjust air to achieve desired angle. Check side to side level and adjust as needed.
Mostly it is personal preference. Try different pressures. I'm currently running about 45 psi.
2012 Forest River Sunseeker 2300 Chevy