As Lutz and David have already mentioned the Romantic Strasse is a wonderful area. We have done the route back to Calais from Austria many many times with just the car or the last 6 years with caravan.
If you would care to look at the website I have just built http://www.dvthompson.webs.com/joysofcaravanning you can view the different routes we have taken back to Calais with sites en route. Leaving Southern Austria we go to either Mondsee near Salzburg see Site no 13 in 2006 trip or Bertchesgaten site 4 in trip 2009. Then you can either go along to Innsbruck and north up the Romantic Strasse or further east up around Munich to Rothenburg Site No. 16 in Trip 2008. From the Romantic Strasse you can go up to stop on the Rhine and Bitburg as we did in 2009. Hope you get some tips from the website that will help. As you see we go out of season and visit nearly all ACSI Camping Card sites at 11 to 15 euros per night. If you need any other help let me know. We are off there in 10 days time but will be on the internet throughout the 12 weeks we are in Germany, Austria, Switzerland and Holland.