We set up our address with MyRVmail.com (who also handles Good Sams mail) approximately 3 months prior to setting up our domicile in early September. It's located in Crestview, FL (Okaloosa County). Need 2 statements (we used Bank accounts) showing the new Crestview address so this takes time.... Also Passport and Drivers Licences (we also took our birth certificates and SS Cards just in case). Only took us 1.5 hours to obtain our drivers licence and across the hall to set up our domicile with full voting rights! We used the DMV office at the County Office (recommended) in Crestview and not Destin. It was surprising easy.
Prior to choosing Okaloosa Co, I called the DMV office and the agent I talked to was familiar with the MyRVmail.com address. Again, it was surprisingly easy to set everything up. We didn't register a vehicle during this process. I was kinda concerned because of issues I've read of those setting up with St Brendan's Isle.
So far, everything is working out fine.