Good morning Carrie....Dakdave gave you some pretty good advice. I would also air up all tires to 100 # to start off. Kudos to you for recognizing the importance of proper inflation. Having your tires properly inflated will result in a better, safer ride, better fuel mileage and better tire mileage. In addition:
1. Check tire date codes. See link below. The date code most likely will be on the INSIDE of the tires. Check all the tires and write down the date codes for each one, noting their position on the coach.
2. Get your coach weighed full loaded for travel. Full fuel tank, 1/2 fresh water and all the 'goodies' you'll take with you when you travel.
3. There are many places to weigh your coach. I fuel at Flying J truck stops so I'll present them as an example. Drive in using the truck lanes. Fuel up and when you pay, tell them you want to weigh. Drive around to their CAT scale and pull up onto the scale. First time you'll probably need a spotter to get you on the scale correctly. The scales come in three segments. Place your steer axle on the first segment and your drive axle on the second. You won't use the third as you don't have a tag axle or trailer. Make sure your coach is in neutral. I chock the wheels, but most scales are perfectly level. Once positioned, you'll need to press the "Call" button which is on a post outside the driver's window. This calls the attendant and they will tell you when the weigh is finished. Pull off the scale and go inside to get your weigh slip. Cost is $10. Hint: If you tell them beforehand this is your first weigh in, they'll be more patient and helpful with you.
4. With weight ticket in hand, you'll see how your weight is distributed in your coach. Refer to the tire pressure guide linked below and fill your tires to the correct PSI. Remember to maintain the same pressure across each axle. That means both front axle tires should be the same pressure and ALL four rear tires should be the same pressure.
Four corner weighing is the optimal way to accurately weigh your coach but it's more expensive and harder to find someone to do it. Weighing as above will give you a pretty good idea and keep you safe.
Finally, after doing all this, get yourself a tire pressure monitoring system, TPMS. This device, IMHO, will serve you well. What it does is monitors your tire pressure constantly giving you a real time picture of the tire pressures. I have the Truck System Technologies system and really like it. Besides the tire pressure, it also gives you the temperature. This provides you with more information about your tires. A high temperature could mean a stuck brake caliper or other issue with your tires. Good luck and drive safely.....Dennis
How to find and read a tire date codeTire inflation tables - scroll to your tire size