Have you considered using these,
Cheap ferry tickets, online ferry booking - LD Lines , always handy to keep moving whilst asleep. It does not work out much dearer than the Tunnel if you book bikes and cabins early,and you save on fuel.
We will be here
http://www.camping-rendezvous-moto.com/ on the 9th/10th July on our way home, the bridge at Millau is well worth a look at.