I assume you're talking about the air bag suspension? (Ed-Helen may be thinking of tire pressures, and sun shining on the tires on one side can make those warmer tires read a few PSI hither than the cooler tires.)
If the air bag suspension is not airing up on one side, causing the coach to lean, I would first suspect the ride height control valve on the low side rear. These valves let air into the air bags when they are too low, and vent air out of the bags when they are too high.
Most coaches have three ride height control valves: one up front that controls the pressure to front left and right air bags (controls the overall height of the front end) and two on the rear (one controls the left rear height, and one controls the right rear height.) The rear air bags not only control the height of the rear end, but also control the overall lean of the coach. If one of those rear bags are not filling up properly it will cause the whole coach to lean.
Possible reasons are the ride height control valve (it is blocked or leaking internally, or the linkage is broken/bent) or a leak in the air bag or associated air lines, or an air bag dump valve stuck open.
Be very careful when working on the air suspension. Even if the coach is leaning, that air bag that is low could be supporting a significant amount of weight. When working on the height control valve or the airbag or airlines, you may cause air to be released which will suddenly drop the coach, potentially crushing you.
Do NOT get under the coach to work on the air bags without supporting the frame on properly rated jack stands. (Don't use the hydraulic jacks, as they can also suddenly drop in a failure situation that releases hydraulic pressure.)
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