I can say with certainty that I've been to many RV parks that use 120/208 Wye services and distribute from there. I really don't think you'll have any trouble at all.
My friend has a motor coach RV that has an electric cooktop in it that only uses a 120 volt circuit, as does the washer/dryer combo. I'm with Tesla: You probably won't see many 240 volt loads, if at all in an RV.
