Zeebrugge to Annecy - which route?

I am towing from Zeebrugge to near Annecy during August 2013 (Sunday 4th August). I was going to do in a day but have now decided to split it into 2 days. Is the view that it is better to drive through Belgium/Luxembourg and if so, is it worth avoiding the Toll roads when dropping back into France? The Via Michelin site seem to only add just over an hour to the journey but i am keen to know what it is likely to be in practice (especially on a black weekend in france).

I am hoping to do the bulk of the drive on the first day (say 7-8 hours) - any good site recommendations for a stop?

Many thanks