I've never done this sort of thing - not sure I know what the operating hours is like, but having driven from just north of Barcelona to Calais in about 18hours, (800miles or so) as a solo driver, I can say it is brutal - I had to catch some sleep about 2hours out of Calais as I was flagging - I have also driven from just outside Krakow in Poland to Calais in about the same sort of time, but 2 drivers and a stop at the Carrefour on the Polish side of the German border for supplies, but that was fairly easy going.