Our class C has dual rear wheels. When we are parked at a site, do we need to place leveling blocks under both tires on each side, or is it acceptable to block up just one tire?
I think the question posed by the OP was whether or not both left and right side needed to be on blocks, not if both front and rear axle on one side needed to be on blocks.
FWIW, I don't put blocks under the left side tires if it is the right side that needs to come up to make the trailer level (or vice versa). That would just require 3 times as many boards or leveling blocks without changing the load on the "down side" tires IMO.