Marcus,
The What Towcar website gives your car/van combination as a good match. Last week I followed a C5 with Bailey Pageant Bretagne along the A10 towards Sandringham CC and we had trouble keeping up with it and we were solo at the time.
I have colleagues and friends who have C5's and none report any real issues one has 75K on the clock. The ride is met to be exceptional.
Regards Monkeys Husband
I have towed with a 22 HDI MANUAL for 3 years now, with a 'van of just under 90% ratio.Absolutely no problems, very comfortable and quite economical if you keep speed below 60 mph. Great on the continent, service is cheap compared to UK.
Don't know about the automatic, but I have seen them towing in France. Make sure that you change the transmission fluid MORE often than recommended! Don't think you will have any problems with your Pageant, but why not get a manual? (If you do, remember to disable the ESP when pulling away on loose gravel up a slope!
Bill