We will be at that site for a week in late august[22nd]although not towing!seems quite a busy place, do not know if its a newish site, although a couple of years back they had all new statics and bar the very high season,the prices were extremely good in comparison to other lake sites. seems to be set a few hundred meters from the lake, no bad thing really.
Routes, the most cost effective route, tolls distance. fuel, would be to head from Calais[if you haven't booked the crossing yet try Norfolkline[Dover Dunkirk] towards Luxembourg all dual carriageway/m/way, down to metz across to Strasbourg, [tolls] and then down to basle, and through to Italy above Milan.
There are variations you can do on this route but this would be possible the most suitable for towing, price, and time/distance