First trip in a city car through France and a tank range of 200 miles. From Boulogne to Mulhouse in a 1 day via Reims not using toll roads. How frequent are the petrol stations?
You shouldn't have any problems. Cheapest petrol at Hypermarkets / Supermarkets - found in most small towns etc. Also petrol stations on main roads. Sunday travel can be a problem - some Supermarkets won't be open / some only until 1pm.
Can pay by credit card at the "window" - might not be able to pay at the pump automatically - some petrol stations can provide petrol 24hrs a day but might not be accessible to UK credit cards. (hope that's clear???)
Just had a look at your route on the AA - 429 miles so a few petrol stops I should think. Looks like you are going to be going through / around several small towns so petrol shouldn't be a problem - just don't leave it too long before refilling.
Thanks for your replies Machecoul and Gef, i`m giving myself 12 hours to get from Boulogne to sorthern Alsace for as cheap as possible, hope not to use toll roads. This is something of a challenge as a lot of my friends say it`s somewhat impossible. We will see...