Tire pressure

I am able to calculate it for you .
Already know now AT pressure of 80 psi ( wich is not the maximum pressure ) but need maximum load of tire and maximum speed of tire.

From you rig already know configuration and that is front 1 axle 2 tires on the road, and rear 1 axle and 4 tires on the road.
Need Gross axle weight Ratings ( GAWR) and also give GVWR ( V for vehicle) and speed you wont go over for even a minute in your use.
Better would be real weighed seperate wheel(pair) loads fully loaded , so inclusif persons.

Advice I give is with some reserve, and officially for filled at 18 degr C/65 degr F. Whenn verry hot outside , as you mention, you should read higher cold pressure ( inside tire temp= outside tire temp). Give the ambiënt temp when you read the pressure or fill the tires and I can recalculate the to fill pressure at that moment.

Normal dually setup is for the valve stems on the outer tires to face inwards and those on the inner tires (and single fronts) to face outwards. This allows for any of the wheels to be used in any position if needed—and, more to the point, for a single spare to serve for everything. The wheels, as you can easily observe, are very heavily dished, and each of the pair on a dually have the dishes facing and both are over a single set of lugs on the hub.

You pretty much need a dual-head air gauge (and probably filler chuck). The forward-pointing head is for the inner tire, and the backwards-facing one for the outer tire. You may also find it convenient to get short valve stem extensions (an inch should be plenty) if the wheel or wheel simulator gets in the way of the gauge/inflator accessing the valve stems. Most of these short extenders are "airless" in that they have a plunger through the middle and only depress the valve in the stem when a gauge or chuck or whatever is applied to the extender; this helps prevent leakage.

80 psi cold is not at all uncommon for the rear tires, and is based on the axle weight. The fronts are typically somewhat lower (as there is less weight carried on the front axle), and too much pressure in the fronts can cause poor handling.

look on driver door post it right there max 80 rear 65 front

The outside dual tire stems will face inward, unless an adapter is installed to turn them 180 degrees. Flexible adapters work. Some wont use them due concerns of leaks. I've had them on 3 different motor homes over 18 years and had one leak. It is possible to have solid "U" shaped stems installed, but then you have a problem if you have to move the tire. The outside dual is the one I usually use if I happen to experience unusual wear on a front tire. Camping World sells a solid "U" adapter that screws onto your inward pointing steel or brass stem. Don't have any experience with them.

The tires have a DOT date of 2010- installed the early spring of 2011; I bought the camper fall of 2011. The tires are in great shape. They are Goodyear tires. Is it normal that the valve stem on the rear outside tires face inward?

The tires have a DOT date of 2010- installed the early spring of 2011; I bought the camper fall of 2011. The tires are in great shape. They are Goodyear tires. Is it normal that the valve stem on the rear outside tires face inward?

80 pounds cold means 80 lbs before driving after sitting for at least 4-6 hours. Air temp has nothing to do with it.
All stems should face the same way. That way no matter what position tire goes bad the stem is correct when you put on the spare.
If you want to adjust your air pressure to other than max YOU NEED TO WEIGH THE RIG FIRST.
My worry is how old the tires are on the rig not the air pressure.
SO HOW OLD ARE THEY