Cycle insurance that covers bikes locked to car mounted cycle rack?



Just wondering if there are any companies that offer specialist cycle
insurance, that would cover a bike physically locked to a car mounted
cycle rack, over night?

Am thinking of doing a 3 week road trip, with bike mounted on back of
car. Which would mean it being attached to back of car overnight.

Im sure some of the suggestions might include using car or house
contents insurance that might over covereage, but I seriously doubt
those particular policies that I have would cover that... at least
without some silly excess that wiill amount to several hundred quid,
that is a substantial proportion of the bikes cost itself.

ta for any help :)