Suddenly, rangetop burners not getting propane..

Could be a p-trap in the propane feed line to the range and is filled with oil. I have seen this in the past and it was a problem when cool at night but not so during the heat of the day. At the time I assumed the viscosity of the oil changed with temperature. The most likely place for the trap is where the copper line connects to the propane distribution manifold below the floor of the RV (ie outside)