Help with planning our route to France

I would be very grateful if any one could offer us any advice on our route to France next year.  We have been travelling there for a number of years with a motorhome and now have a caravan.  Since we bought the caravan we have done more stop-overs en route for re-fuelling etc but are thinking of taking the overnight ferry from Portsmouth to Caen next year to make life simpler and cut down on the number of times we have to stop-over/unhitch/hitch-up.  The main problem with this (apart from the expense!) is refuelling.  We shall be travelling from Cambridgeshire to Portsmouth and then from Caen to a campsite near Le Mans for a couple of nights before travelling on further south.  So where would be a good place to refuel whilst towing a caravan, especially on the UK leg of the journey?  Any advice be appreciated.