I asumed that it was propane, it is sold at some gasoline stations too, should it be gasoline then there is a leak along the line and it would smell even after the RV has been standing for a while, gasoline smells very different than propane, it is helpfull for those of us trying to help if the OP explained what they where refering to.
As I stated at the begining of the answer I ASSUME the OP does not mention if it is GAS as in PROPANE GAS or GASoline as in the fuel used in the motor.
navegator