I had the same problem at our insurance agents, in Canada, with our used Roadtrek, they wanted to insure it as a bare van through the VIN number.
I tried to explain that it was a bit more expensive than a bare van, they responded that they were not interested in what had been done in finishing the interior of the the van!
I managed to get one of the staff to get a quote from Aviva or Progressive who seemed to know what a Roadtrek was! Aviva came back with an acceptable quote and I have been with them for several years.