There's definately some good deals out there if you shop about.
Similar story with my Transit tipper ( Yea I know it isn't a Roadster
)
Most of the insurers would only accept no claims earnt on a commercial policy
Gladiator, Mirrored the maximum no claims entitlement being used on my daily driver.
After the first year the renewal notice showed maximum, earnt commercial no claims disscount.
This left me free to shop about, I managed to get a Direct line commercial policy with a named driver + unrestricted carrige of own goods & goods associated with my son's roofing buisnes ....... All for the princely sum of £146 TP + F&T
The above is not conditional on me owning another vehicle !!
Shop about folks