Leave the jacks up. It will take bit longer than what you described to cause the tires to flat spot. If you really want to get the tires off the ground jack stands are a better option but you always have to have a backup plan other than the installed jacks to get the coach off the stands if there is a problem.
Plywood is probably OK to get the tires out of the dirt but what might work would be to cover the wood with OTR trailer mud flaps. Usually made from recycled tires and not very expensive. Three will work. Cut one in half from the front wheels.
The off level area you described shouldn't be a problem for the coach. I would alternate which side is on the down slope. Your drive axle wheel bearings could be lubricated by the differential oil and if it sits long enough and slope is great enough one side could dry out and rust given the right conditions and time. A monthly drive and generator exercise would reduce the potential problems sitting could cause.