You would have to personally check with your local laws and regulations in your county and state but if the land you're living on in your RV is rural land then you can usually legally live in the RV on that Rural land.
Some towns and cities may have regulations that forbid living full time in an RV on your land unless it's in an RV park.
But if you plan to live full time in an RV I would purchase land out in a rural area where no one else is around so that they won't bother you.