Hagerty pretty much told me to get lost with my 9500 GMC and my M-817 5-ton. You might try
Gulfway Insurance. I ended up going with them on the dump truck and the road tractor and they were very good. You might also try your local State Farm agent. We had a late model (non-collector truck) F-450 landscape truck that we used for our farm and compost production operation (speaking of going up and down the road hauling manure ...

). We insured it as a farm use vehicle and State farm was easy to work with and offered a reasonable rate for a medium-duty working vehicle.
Regards,
John