Thank you all very much for getting back to me.
We will be staying in Soussa for the week but it is our intention to use the car to go to both the more visted and, it appears, more accessible places (Carthage, Tunis, El Jem), but also would also like to have the ability to get out to the further out areas (like Dougga) and have the ability to stop off at little villages we might pass through or just drive around an area to see what is there.
I guess the main concerns I have are:
1. how accurate are the reports that even cars from international companies are not well kept. I realise that every country has its local 'elements'.
2. assuming all new hire cars are unleaded (?) how available is this?
3. would it be worth it, taking into account the info from roundasapound about rates, to have public transport to some places and get a car for other longer trips on an ad hoc basis.
4. SMa, you mention hiring a taxi for the day. Sounds like a good compromise. Is this as safe as 'common sense' dictates?
thanks again in advance