as you know Kev we always "do" France every year with motorbike in tow.
Never been that early in the year though and we always stop at campsites anyway.
If you are going to Dunkirk then its a bit of a trek WEST to do the WW2 Normandy landing sites etc..
think that you would be best off doing Portsmouth to Caen really with Brittany ferries (a nice overnight crossing)
Anyway.. enjoy your trip and don't forget to stock up on some good old British bacon before you leave as the froggies equivalent is just some wafer-thin shite ham stuff