Just to back up Lee and Steve, I dump almost all air when parked for storage, and did so just last night. The lowered entry also helps the wife negotiate the stairs while loading and unloading. I learned my lesson when new to the coach, and watched as windshield cracks developed and spread over weeks while just sitting by the house. Turned out the windshield had been improperly mounted at the factory, but nevertheless you should park the rig balanced. One airbag's slow leak is all it takes.
I also minimized body twist by releveling my partly gravelled pad. Airbag leak or not, you don't want one axle end lower or higher than the other three together. As long as two on one side are relatively level with one another, or two across the back or the front, it is fine. In my case the front is very slightly uphill, but both axles are nevertheless level side-to-side.
Off topic a bit, it also helps roof drainage, since I've discovered my roof when level forms a small "lake" in one spot; that revealed itself a few weeks ago via a leak through a hidden solar wiring seal fault at the edge of the lake - it acted like a tub drain during an Oregon downpour while the rig was parked level at a service facility. Ideally I'd prefer a covered port here at home, but there just isn't room for support posts along the already snug confines.
Joel