A different perspective from Canada...
I'm in Nova Scotia and bought the bus already converted. It's a schoolbus converted to a motorhome/racecar hauler (enclosed 16ft back with ramp)
Called the ins company the guy before me used...no way, it wasn't pro done!?!? It was a BUS and nothing I could say about it. Went to "silver wheels" which ins hot rods/antiques/etc. NO WAY, not a pro job. A wife of a guy who works for me is in insurance, she fought for two days and we said whatever they wanted to finally get ins. Got it for the 6months I was going to have it registered (racing season) was $600. following year, THEY won't cover it because it's not pro done!
Just to be clear, there are a dozen or more buses running around the Maritimes hauling racecars. Went through several companies and back to this same one for a last kick at the cat because racing season was about to start. Had to get an appraisal. Fine, buddy appraised it at $19,500.....um...they charge so much per value so I got him to state it was worth $12,000. Sent appraisal, registration (which in NS it's classified as a camper) and the girl said "oh, it's registered as a camper?, oh in that case it's $128.00 per year for full coverage, pl/pd/theft/fire/glass/etc"
I put ins on it and will never take it off now.
Even if it's only registered 6 months out of the year, I leave full coverage on it all year round now.