Hello from swansboro,nc.
Didn't have any insurance problems with nationwide and a few other skoolies have called my agent and got covered with no problems.
The only issue I had with a place to work on,park my skoolie was in my own driveway and a man in the neighborhood didn't like it and called the county for an abandoned vehicle.
County land use came out and to make them happy I had to insure,register way before I was ready to put tags on it and I couldn't have construction material in public view.
After that the man kept calling and complaining and the county offered to take him to court because it was not an abandoned vehicle as long as it was insured registered and in a driveable condition.
The county I live in has busses for sale now and they are well maintained and you will get every stitch of paper trail from the day the bus was ordered. Build sheets,wiring diagrams for chassis and body,full maintenance records from day one to present.
All that sounds good but there are few catches if your looking for a fully mechanical/no electronics bus.
Don't know what type of bus you are dreaming/looking at yet.
Hope this helps.