Just checked craigslist, and only 5 of the 31 MB listings were 12-month leases. And of course full-time AirBNBs would not be on craigslist.
To put it another way, do you know a single person who is a long-term full-time MB resident, either as an owner or a renter? I have never met such a person in many years in San Diego, and I live nearby in OB and am social. You’d probably have to go back to the 70s or 80s to find many such people.
