IIRC from GCSE physics, heat can transfer by conduction, convection and radiation. So when the car is moving I'd expect heat soak to be reduced for conduction and convection, but not eliminated. Also as radiation heat travels through a vacuum (sun's heat to earth) the heat 'reflectivity', as well as the specific heat capacity, of the materials must also be a factor in heat soak, whilst in motion.
It's been a while since I did GCSE physics, so that could be wildly apocryphal
Edit: typos, sorry for sub GCSE English skills