I'm going to chime in here..........as a cop.
The following comments are just my opinion, and I make no claim that they are all encompassing, and cover every little nuance that individual state laws address.
Legal in your specific area or not, I would not allow anyone to consume alcohol while I was driving, and the RV was in motion. That being said, I would not for a second worry about open bottles that are capped, and stored within the living areas of an RV. I also would not worry about empty bottles that are clearly in a trash container.
While states manage their own alcohol laws, the Bill of Rights is always applicable. You are constitutionally protected against illegal search, and seizure, no matter your location in the United States of America. At the end of the day, if an officer wants to search, short of some exigent circumstance, you MUST provide consent to search or a search warrant MUST be obtained. You have an expectation of privacy in your domicile. An RV certainly qualifies as that.
Happy camping, and have a drink for me,
Jeff