Read here.Here's one from IowaIndianaIndiana and Iowa are pretty much the same. I don't have time to search every state, but do a Google Search on... for example... Oklahoma Open Container Law. and you'll have your answer:
Exceptions
Certain vehicles. Passengers can lawfully possess an open container of alcohol in the:
passenger compartment of a motor vehicle that’s used primarily for the transportation of persons for compensation (like a limousine or taxi), and
living area of a “house coach or house trailer.”
However, the driver of such a vehicle is still prohibited from possessing open containers of alcohol.
Oklahomabut it looks like there is no "exception" in Oklahoma for RV's. It' snot mentioned, so in this case, I would assume an RV fall into the same category as an automobile.
Best advise I could give you, keep the alcohol "bottled up" until you reach your destination.