Harry, I know your neck of the woods very well, Mrs Joe hires the Tramper at Bottalack, we’re down there 3-4 times a year. Don’t know about insurance, but we almost bought a motorhome last year and we were planning on getting a hire car for a few days when we were down there. I found a very cheap car rental company in Cornwall, their cars aren’t new, but they are cheap. Not sure if it helps but have a look at this company.
https://abhire.co.uk/cars-prices/
Enyaq EV