RR's & Bentleys seem rather odd if one looks at the 'building' logic. You have a mix frequently of mild steel and alluminium panels. Typically on later cars a steel monocoque body and aluminium doors, boot and bonnet. Earlier cars with separate chassis cars cars can vary. It couldn't have been for ease of construction (steel would be easier to manufacture presumably) - doubt if it was for weight saving (most people would never open a bonnet and most likely have flunkys open doors for them) - understand the use of hand rolled and formed aluminium for short production runs and the costs of producing the large press tool required for some panels..........its the poor rust protection that seemed to plague the Silver Cloud and S series cars that surprises. Even the 'interaction' between adjoining steel and aluminium panels that seem to plague other high end manufacturers RR seemed to deal with OK.