Dave,
When I was in Germany last year I asked some of my german friends about the city....They were sure it was FillingeN not FillingeR. They said they couldn't find the latter. Fillingen is in southern Germany very near the French border. Also they said that Kunagunda (his wife)was a very popular German woman's name in the 1700's and 1800's. Fillingen has a web page.

Ken