Technically you are not using your car for work, you are commuting to a place of work.
If you were using your car for business deliveries, or taxiing people around for money, trading as a mobile mechanic etc, then fair enough, you are using your car for work. But just driving your gear to a gig is surely commuting. While you are working (gigging) you are not using your car.
Also, and this is never easily accepted, but insurance companies don't find a get out anywhere near as much as people would like you to believe. In my 35 of being in the insurance repair trade I can't even think of a handful of times when they weaseled out. Usually you simply pay the extra that the relevent cover would've been before we're allowed to repair/release your car.