Hi Davy; Welcome to Permies!
I don't think anyone in Spokane has gone the legal insurance route.
I do know, that Portland has had insured builds.
To attempt to get any insurance. Your RMH must always be referred to as a brick masonry heater.
Most locals require a licenced mason to build one. Some locals may not.
I suggest a brick bell rmh in the new batchbox design. All brick and with a closed door while running.
It could... be insurable.
The original J tube rmh that you are reading about. With the open
feed tube and exposed flame ... chances are they will laugh mightily and not insure it.
Most of us with rmh's either live in unincorporated areas with no regulations.
Or they just build one anyway and not worry about insurance.( I am not suggesting this ... only pointing it out.)