Do you want to keep moving (different place every night) or ride somewhere unpack and explore the area?
If the latter I would recommend Ardennes/Eiffel Mountains area, stay in somewhere like Aachen, Trier or across to Koblenz (do a search for bikers guest houses or stay in smaller towns). The roads in the area are fabulous, you can do the Nurburgring, Spa, Mosel river tour, Luxembourg, WW2 battlefields etc etc. Belgium for the pomme frits and Germany for Beer, Bratwurst plus cake and coffee at 3pm.
The area is an easy days ride form the Channel or Dutch ports
Alternatively go to the Harz Mountains, about an hour south af Hamburg, which is very biker friendly with fantastic roads. It straddles the old East/West border with lots to see and do.
Check out [size=78%]
http://biker-hotel-harz.de/[/size] run by Chris and ex MCN?Classic Bikes Journalist .
The Harz are also an easy days ride from the dutch ports, bit further from the Channel ports though.
For both areas I use the Hull to Rotterdam or Harwich to Hoek Van Holland overnight ferries.
Good luck
Kev