We have noticed some rocking on our 4-jack Class A. I don't believe it can ever be totally eliminated, but here is one technique we tried, and it has helped in the situations described.
When parking on non-paved surfaces (even compacted dirt/gravel) for longer than a few days, my wife and I both noticed that the coach seemed to rock more the longer we were there. Our theory was that the metal pads at the bottom of the jacks (fairly small surface area, especially at the front) slowly created small depressions in the ground over time, allowing more movement than when we first parked. To reduce this 'depression effect', we cut 12" lengths of 2x12 wood and place them under each jack when setting up camp. This increased the footprint and has reduced the rocking during extended parking periods.
Unlevel parking areas also seem to cause more rocking. The 2x12x12 wood jack pads are used on unlevel sites (regardless of the surface) to reduce the travel required by the low side/low end jacks. This seems to help by reducing the jack's 'lever arm' length, thus making the parking stance a little more stable. Occasionally we stack two blocks on each other (for the low side/end on unpaved uneven surfaces), but never more than that. We have also used them under tires on the low side (single blocks only, put in place while moving the coach the last foot or so into the parking spot).
To create these blocks we went to the local hardware store and bought an 8' long 2x12, and used their free cutting service to create 8 jack pads.
There may be commercially available jack pads that perform these same functions. We came up with this solution while on a trip and made use of a local hardware store.