I presume you intend to stay in a hotel rather than camp in northern France in winter? If you are taking the route south via Rennes/Toulouse you could do a slight detour to St Malo. You should get there in about 3 hrs from Cherbourg. I've stayed a few times in the Ibis St Malo Plage hotel, which is fine, and is near the town centre. You can pay for parking at the hotel but I've had no problems parking outside in winter. There's also a municipal car park a few minutes walk away. If you don't want to detour, you could try Avrances. There is an Ibis there, it used to be an F1, and has off road parking. But there are loads of others around.