fulltime

You don't just register your rv in South Dakota, you attest that you want to become a South Dakota resident for EVERYTHING including state income tax, banking, insurance, etc. Then you can register your vehicles there including your RV. You will need to give up being a resident of any other state which likely would have an impact on your property taxes if you own real estate in another state.

If your question is related to becoming a fulltimer, you might want to look at the fulltimer section of the forum.