E40 to Gent, either via Antwerp+Heerlen, Brussels+Heerlen or Brussels+Liege* to Aachen, A4 to Koln, A3 to Passua, A8-A25-A1 to Wein.
You might want to bypass Koln on the A61-A48 route, which adds 7km.
Other than through Belgium and if you want to bypass Koln or not, there's only one sensible route.
*via Liege is 2km more and simpler, but a bigger place and not as nice at Aachen. The Antwerp and Brussels via Heerlen are the same distance and not much to choose between them.
Dankeschoen, actually my family are travelling by coach and will be in that minority who will be using the Channel ferry over the tunnel. I had a feeling you would cross Belgium ans travelling through France and then Germany would take longer and, of course, the tolls would add to the cost of the holiday.