Tire pressure for new class C

The door pillar recommendations would be a decent starting point; they're set assuming full gross weight load on the axles, and that's often not too far off for a class C. I would guess that it's more likely for the front axle to be well under gross, and proper inflation there (avoiding overinflation) is rather more important to good handling than on the rears, so when you get a reasonable chance to weigh the motorhome it may be worthwhile to adjust the pressures if the axle is well under gross. It's preferable in my opinion to have a little more pressure than necessary than to have not enough (assuming one isn't going above the maximum pressure ratings of the tires or wheels, of course).