Our inverter is always on. (We turned it off once and ran down the coach batteries.
)
And yes, landing pads are a sometimes good idea to help keep the jacks from hyper-extending, depending on the slope. Sometimes you might need them under the tires, too. In that case, make sure they are big enough for the entire tire to sit on them; you don't want the edge of the tread hanging off or you might damage the tire. (And if you ever use them on the back tires, put supports under both duallys.)