Best material to park a 33 ft RV on grass area over winter?

Make sure you wait to move it until the frost is out of the ground and it is drying up from spring rains. If not, you will end up buried in mud like we did our first spring. Ground looked ok, but as soon as motorhome moved, grass gone and gushy slimy mud right under the surface. Yuk - hope to never repeat that experience.