Then I disagree with part of the Which? article!
For both car and caravan, a fault apparent in the first 6 months is easiest dealt with under warranty. CRA doesn't need to be even mentioned if the supplier/customer relationship is good.
Where a car/caravan has been bought from a distant dealer, it's often not easy to use local dealer for caravan warranty work but it's straightforward for cars.
I would think that any repair within the first 6 months automatically falls under CRA 2015. A customer is unlikely to go to a dealer and state under CRA 2015 they want the repair done.
It is just assumed that the work is done under warranty which is why either the 30 day or the 6 month period can be extended as the repairs are covered b CRA 2015 anyway.