Thanks for your reply.
I've very limited experience of driving abroad - I usually either fly or take the train - so I'm not the best person to ask about the availability of Formule 1 rooms. I guess that you might get accommodation by simply turning up on the day but it would depend upon such things as whether there was a major sporting event on in Rouen.
However, even if one hotel was full, they've got a centralised booking system, so they might well be able to direct you to an alternative Formule 1 hotel along your route. (There are loads of Formule 1 hotels across France and, indeed across large areas of Europe. There are even a few in the UK).
Chris