Thanks all, so far...
Our vehicle *is* a registered motorhome, (in)conveniently in the faraway state of Maine.
Technically having the vehicle there isn't a problem, it's the hookups. We're not even using 120v/220v large-size hookups, just extension cords to house wiring and a hose for our sink.
These things constitute living a vehicle, which is the prohibitive part. We're going to attempt to dub our bus a 'work space' but unfortunately that might imply a perpetual paranoia of aforementioned complaining neighbor. We are trying to finesse a rebuttal to her outlandish claims, which included us "using the bathroom in the compost" (??!). That gives a portrait of whom we're up against, and with luck the city could share our opinion if we play our cards right. We're actually here beautifying, garden-ifying, and caretaking a second lot on our friend's property: so even 'visiting' doesn't cut it necessarily, but "work studio" seems the best option.
Mostly, we're interested in anyone's ability to confront/appeal/parry ordinance trouble. Seems doubtful without the paranoia ingredient. Le sigh!
Thanks for your replies, and of course future solutions