In reply to Samuel Palmer:
Be careful. First stop just outside Capetown (for self-catering supplies etc) we were spotted going to a supermarket. Locked the car using central locking - definitely). When we returned everything had been nicked from the boot (gear, cameras - everything).
On reporting it we were told by the police that this is 'common' just outside the airport. Hire cars are targeted (e.g. at supermarkets): as we got out and clicked the central locking key fob, some guys operating a device which effectively neutralised the central-locking (don't ask me how - others might know...).
Net result was that none of the insurances would pay out as there was no evidence that the car had been burgled - no sign of forced entry. In spite of a letter from the local cops, we kept drawing a blank (over £4k written off)
So - (i) check insurances and ask them about such incidents (SA police said they are 'well-known' ploys) and (ii) leave someone in your motor when collecting the beers!
Maybe we were just unlucky - but better safe than sorry
Have a good trip