Real cause of "rivering" or cupping? Air pressure?

You will need a larger than "Average" shop to do this kind of work. I had a really old shop - one that was established in 1953 work on my 97 Bounder. The front end of Ford chassis have axles that are "adjusted" by bolting them down to a large I-Beam, and using a 10 - 15 ton jack to change the angle of the axle, so that the tire starts standing straight up, and not leaning inward or outward. The factory specs say that it is 'not adjustable' and anything between 1* to the right or left is 'fine' and within tolerances.

This is a very heavy duty front axle design, just like used on trucks way back in the 60's and 70's. It has proven very reliable, and once properly adjusted, your tires will last a really long time. My front tires got over 42,000 miles on them, before replacing them at 7 years old. Still had about 1/2 the tread left on them. I only had one alignment when the RV was new, and had it checked again at around 25,000 miles because I was having a problem with my car being towed behind the RV, ended up the RV alignment was still great, and not needing adjustments.

Your tire pressure will increase with temperature. This is why they say to check it 'cold' or within say 5 miles of starting a drive. So if you check it at a campground and find it is 85 PSI, and should be 110 PSI, then drive 35 miles to a truck stop, measure it at 98 PSI, and only increase it to 110 PSI, you will find it has increased 13 PSI due to driving, and will only be in the 95-98 PSI range the next morning at another RV park.

Also it will change with climate. Say you check it in Michigan and find it is 110 PSI at 40F. Driving might increase to around 120 - 125 PSI, then stopping in Texas RV park it might read 118 PSI in the morning when "Cold" at 75F.

In this case, if it is 118 PSI at 75F, reducing pressure to 110 PSI cold at 75F is fine. But if you check the tire pressure at a rest area, after driving say 100 or 300 miles, expect the tire pressure to be 8-15 PSI higher than cold. It will increase more on a cold day, because colder air will expand a lot more than warm air.

Good luck!

Fred.

Take your coach to a well equipped shop that has the equipment to check the thrust angle on your rig. I am sure that you will find that the rear end is not in perfect alignment with the center of the coach. If the rear axle is not aligned properly, the front end alignment is close to useless because the rear axle is always trying to push the front end sideways.
Any shop that has the right equipment can do this. The other shops, that do not have the equipment, will tell you that the rear axle is not adjustable(they are wrong) and that all you need is a front end alignment. Thrust angle adjustment