Once upon a time Captain Mike of Westfalia.org described his homemade Westy/camper levelers (good for that Dometic!) so I finally pulled out the power tools and made a set, tweaking the measurements to my own preferences.
I used:
one 2"x8"x10'
20 good wood screws (you can use nails, but ...)
wood glue
First / bottom piece: 24" one end cut straight, the other cut @ 45 deg
Second / middle piece: 18" one end cut straight, the other cut @ 45 deg
Final / top piece: 12" one end cut straight, the other cut @ 45 deg
Line up the straight edges so the 45 deg edges make the "steps"
Wood glue up, screw together on both top and bottom (I used a 5 spot pattern)
Stack together
Stashes nicely in the luggage rack