Every tire make/model has a tire inflation spec table that says how much pressure (psi) is needed to support a given load (weight). If your tires are carrying less than their max load, you can use less pressure and get a softer ride. Thew tire dealer should have (or be able to get) the inflation table for whatever make & model tire you buy. Your job is to get the rig weighed so you know how much weight is actually being carried on each axle (pair of tires) so that the tire load is known.
The inflation shown on the coach manufacturer's placard is the psi needed at max axle capacity. Most coaches are not loaded to the max on the front axle and many not on the rear either. Weigh yours to find out if you can reduce pressure. But until you do, go with the amount needed for the max axle rating. That's probably less than the amount shown on the tire sidewall, which is the for the tire's max load rating.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL