Someone may have already mentioned this - but!
As you know getting your rig level in a poorly layed out parking space makes your jacks work harder and puts "some" strain on them and your frame.
I had a 60X17 foot concrete w/rebar pad put next to my house this spring to keep my coach at home.
I had the contractor tilt the pad slightly (I believe it was 1" for every 10 feet so that water from the winter rains would not settle next to the house foundation.
I was originally going to use some treated lumber under the wheels to help level the coach. After putting plywood on the concrete for the leveling jacks, and finding that it stained, I rejected that idea.
I was at Lowes today and found a decking product called Choicedeck which is made by AERT. The trim boards I used are 5/8"X9-1/4"X12' and can be purchased in either gray or redwood color. The color won't leech, nor will they split like lumber. They also are wide enough to properly support the tread of the tire.
I cut them in lengths of 4', 3' and 2' lengths using up a total of 3 full boards.
Now the coach is level and water runs more effectively off the roof then before.
Retired Coast Guard Chief Petty Officer - DW is the REAL Boss