South Dakota makes it very easy to qualify as a resident. Stay at least one night in a paid accommodation (that includes RV parks, campgrounds, etc.) Bring the receipt from that stay along with the usual ID requirements to the DMV, sign a form that says you'll eventually become a real resident, do the usual driver license stuff, and that's it. No proof of permanent address. It takes longer for license plates to arrive, but mail forwarding services deal with that.
No state income tax (which is cool if you make enough that you would otherwise pay state taxes)
No vehicle inspection
Lower insurance
A down side is that you need to renew your DL in person or use their inconvenient remote renewal procedure. I didn't want to go all the way back to SD, so it was easier (in my case) to change everything to the state I happened to be in at the time.
Another is that SD license plates outside SD pretty much advertise you're a full time wanderer.