Max is 100 psi. I run 70 psi in my Lexi, and check the pressure before each trip. They have a tendency to lose a bit of air over time.
Just experment with the psi until you get the ride your comfortable with, based on your rigs weight and the load your carrying. With a rig your size, I'd start at around 55-60 psi, because of the long overhang of the coach rear.
Be careful when adding air as the bags are small, and it's very easy to "over air" them very quickly, past the 100 psi max.
Grumpy