Our 5th wheel sits on gravel in the driveway an do not level the trailer unless I have to open the slides ... After doing what I need to do an closing the slides I rise the jacks except for the landing gear ... I do not run the frig when stored so the trailer dozen't have to level as it should when your frig is being used ...
As stated by OP I use blocks under my levelers when we run into a camp site with unlevel or uneven ground, however I will not use a camp site that is so uneven that I have my tires off the ground even though my leveling jacks can take it I don't feel I need to put that much stress on the jacks nor my trailer frame ...
Safe Travels :)