The only right way to know the "correct tire pressure" is to have the coach weighed by wheel and then check the tire company's web site and look at their tire weight tire pressure guide.
Now most are going to tell me i'm nuts how can you do this, but it is getting to be the only way to stop some of the tire issues that are all over the internet.
Some scale houses do have wheel weight scales, and Escapees has done it way now for some time.
Hope this helps and Happy Camping
2010 Cedar Creek Silverback 35ts
2001 GMC 2500HD w/ Allison & 8.1