There is no length limit if you join the RAC Arrival scheme - and even if your caravan develops a fault when you are on a site (rather than on the road), the Arrival scheme covers you. Definitely worth joining the C&CC just to benefit from this - we've had Arrival cover for years and have always had excellent service.
The only way they will cover you if you are towing is if you join through one of the clubs. I found this out with the RAC the hard way. More annoyingly, I was a member of the C+CC at the time and would have even got my RAC membership cheaper through the club, had I not joined the RAC before the club. Now with Caravan Club and Mayday. Can't fault mayday, although there was a post here a few days ago where someone said they "trashed" their caravan.
Amazing family weekend with old steam engines, classic car displays, market stalls, and full catering and bar. And camping on site - Save £25 by booking in advance.