Within this link should find your answer for air bags you may have.
You need enough air to have your coach on a level plain and keep from bottoming out over bumps or dips in the roadway.
As far as your tires go you need to have coach weight than follow the tire pressure tables for the weight after you have coach weight with your personal stuff, full gas tank and what ever water you may carry plus LP gas.
Michelin------
Goodyear