Somewhere around 40 pounds seems to me to be reasonable for my unit. I'm not aware of much of a scientific approach to setting them besides just trying things out until you get the ride you want, especially as how much air you need depends on the stiffness and strength of the other vehicle springs. You can get some rough idea from how the suspension sitting and where the vehicle ride height is as you add air. "Level" in the house part of the RV may not be "level" from the point of view of the chassis springs (even if sitting on level ground).
I'm not sure that #7 from Oldme's link is all that helpful for us since there isn't any practical way to unload an RV's chassis once the RV is built. (The RV itself is the majority of the chassis load.) It seems more useful for installation and operation on cargo carrying trucks and similar vehicles.