1in x 8in x about 60 in long will bridge both tires and makes a good support. just stack to height needed. each graduation on my bubble level equals about one board thickness of adjustment approximately. 1 x 6 x 48 may work, just measure tire width and the distance to span across between the two tires, if you have two tires on each side.
Most stabilizers are for stabilizing , not leveling.
there are many ways to level, plastic lego blocks, wood blocks, i like the stability of the longer wood that bridges both tiresl
enjoy your camper
2008 Wildwood LE 29BHBS