Hi Carol or is it Wendolene
My 2 have done to and back from France a few times now in our Twingo boot space. They travelled well (ok as well as can be expected) in a big plastic rabbit cage, into which I fit their bed and a litter tray. I stopped every 2 hours or so to syringe some water into them (not their favourite part). They were well wedged in with other stuff, kept cool with the aircon and they could see out. My friend in France has done the UK-France thing with a very ancient kitty and her kitty appreciated being able to see out as well. They should also be able to see you to minimise the stress. I did the Feliway bit about an hour before travelling, but it did take them a while to settle down. They travel ok though; some cats are horrendous in the car. Have you tried a short trip to see that he doesn't freak out or get travel sick?
If you are going Eurotunnel, be warned that there is no shade at all for parked cars (I complained - no effect) at Folkestone. Peeps can take their dogs into a shady area but cats have to stay in the car. So when I do it again , if I do, I would choose a cooler time of day in case of delays. Coming back, the French officials at Calais were brilliant and came to the car and put their hand with the scanner in the rabbit cage to scan the chips so as to minimise stress. I wouldn't go by ferry because I didn't want to leave my boys unattended in the car below deck during the voyage. Travelling with you I think is the key.
How long's your journey going to be? Mine did 7 hours the first day, stayed in a nice Ibis hotel (that was their fav bit) and then 6 hours on the next day, including stops. We travel/led to the basque area from SE London so it's about 12 hours driving. Most French hotels are great with cats, but I'm sure you know that.
I took along the airline plastic pet carriers in case I needed to 'decant' the cats at some point, but I really swear by the bigger rabbit cage - it has a plastic bottom and is wire with top entry so very easy. Cost quite a lot though! It just fit nicely so there was no lateral movement when driving as you are right, that's NB. Hope this all helps.
ps assume you have a hatchback car? If they were to travel on a seat, I don't think the rabbit cage would fit.
pps don't give him too much to eat before travelling!!