Try 65 PSI in front tires and 75 PSI in rear. No big flat-sided tall vehicle handles well in gusty cross-winds or when big rigs pass you. Don't believe those who say their Class C handles and rides like an SUV after throwing a lot of money and parts at it. It helps to stop every 100 miles or so and walk around on solid ground to relax and get ready for the next 100 miles. Harsh ride can sometimes be helped with removing a leaf from too-stiff rear springs. Beat up concrete interstates can loosen your fillings. Secondary asphalt roads can be a lot smoother with better scenery.
