Add a 30A 126V outlet for M/H (temp) plug in!
The 30A 120V RV receptacle is a rather unique thing.  Since is it 30A, you absolutely must use 10 AWG wire and a 30A breaker.   

However many RV owners can make do with 20A.  A breaker trip is a thing to be avoided. They simply use an adapter/cheater cable to get to a NEMA 5-20 plug.  They plug this into a NEMA 5-20 receptacle, which you will find familiar-looking.   This requires a 20A breaker and 12 AWG wire.   And yes, you can use it for other stuff the rest of the time, or even, at the same time.



NEMA 5-20 Receptacle.  20A, 120V. 

As isherwood points out, load is an issue.  Some RVs have less than 20A of fixed load, and are equipped with the 30A receptacle only because that was the standard for RVs.  Others may be built to pull over 20A, and on those, you'll need to be careful not to activate too many heating and/or cooking appliances.  Of course, plug-in loads can always push you over.  You can plug a power monitor like a "Kill-a-Watt" in between wall and RV to determine what you're pulling.  My Kill-a-Watt will helpfully beep if load is over 15A.  Really caught me by surprise, I didn't know they had audio.