The Michelin tire chart, if you are looking at the correct one, lists the inflation pressure by axle. The terms are steer axle and drive axle. It does not care or list weight by corners as truthfully, those are irrelevant for proper tire inflation. Corner weights are good for loading and balance, however.
Until you get your coach weighed, inflate your tires to the maximum on the side wall. Getting the proper weights and inflation pressures is really pretty easy. First, get your coach weighed. CAT scales at truck stops are easy to find and easy to weigh at. These are three platform scales and you need to put your coach on the first two pads. If you have toad, leave it at home.
Your printout will list two axle weights: Steer axle and drive axle
Take the steer axle weight and divide it by two. Multiply this by 1.05. (multiplying by 1.05 accounts for side to side differences in weight). The resulting number is the weight carried by tire. Look this up in the Michelin tire chart (
Michelin RV Tires | View Michelin RV Tires load and inflation tables for motorhomes and recreational vehicles. | Michelin RV Tires) That is your steer axle tire inflation pressure. Most people add 5 psi to that number. Repeat the process for the drive axle.
Based on your numbers you posted, Your fronts would require 75 psi + 5 psi or 80 psi, your rears would require 70 psi + 5 psi or 75 psi. For practical purposes, tires should not be inflated less than 80% of their maximum rated load. I would increase the pressures to 90 psi in the front and 85 psi in the rear.
Your guess at 90 psi was a pretty good one and you could, if you want, lower the rear axle to 85 psi.