There is a difference between a liveaboard and a full-time cruiser. Liveaboards can often use their marina as a legal mailing address and such. Full-time cruisers can use a mail forwarding service like St. Brendan's Isle
Most states require some proof of residency—often something as simple as a utility bill at an in-state mailing address.
We use Saint Brendan's Isle as full time cruiser's, but we also used SBI while living aboard at the dock too. At some marinas that don't post that they allow liveaboards you can be accepted if you do not use their address. We also found that it was far easiewr for us to change marinas at whim without the hassle of requiring an address change when all our mail and official residence was with St. Brendan's. Take care and joy, Aythya crew