30 amp RV service is 120 volts. 50 amp RV service is 2 circuits 120 volts each this is actually a 240 volt service at the outside circuit box. Inside the RV circuit box divides 240v into 2 circuits 120v each. There are no 240v appliances, HW heater, AC or Heat units. Everything inside the RV is 120v.
Our RV has 30 amp service. The RV uses only 1 wire to the circuit box so there is only 120v to ground. The other 120v terminal is not used. There is no 240v only because the other phase wire is not there. The 50a service has both phases but keeps them both separate for 2 circuits that are 120v each inside the RV.
Years ago I took a volt meter to the camp ground 30a service is 120v on 1 terminal. 50a service is 120v to ground and 240v between the 2 hot terminals. It appears to be a normal circuit like for a 240v, welder, kitchen stove, electric dryer, but inside the trailer it is wired 120v. RV circuit box uses a different plug you can not plug in a, welder, kitchen stove or electric dryer.