We went full time 3 years ago and are using Americas mail box near Rapid City. They can guide and help you get set up. After that you really don't need to return until your drivers license expires, or once every 5 years. When we joined we had a 5th wheel. In Minnesota our plate was $50 dollars a year, in SD it went up to $120.00 a year because SD goes by weight when registering rv's. However when we bought a new rig the SD sales tax was 3% much better than most states. Another plus is when you get a license you will have it when you walk out the door. You don't have to wait for it in the mail.
We have now bought a home in Minnesota for the purpose of flipping. Owning a house in Minnesota as a resident of another state is like having a second home at the lake. I'm sure many states are like this we just can't homestead the house and pay a little more in taxes.
Having said all of that we spend over 6 months of the year in Texas.
We still pay taxes to Minnesota because we sold a business and hold a contract on it. So for us it was all about a place to send our mail.