I also got Allstate insurance via Kelly Newsome, but: I was not able to get RV insurance until my bus was registered as a motorhome in Vermont (which took a month and a half for various reasons). I was not able to find any kind of insurance at all before this - "commercial vehicle for personal use" policies are not a thing in PA, and insurance for a school bus proper was ... prohibitive.
State Farm told me they could offer RV insurance if the bus was registered as a motorhome and also they had inspected it themselves to verify that the conversion was complete and all the motorhomey functionality was provided.
Since you're doing a one-time move, I think it's possible to get temporary coverage for a couple hundred bucks.