Warranties aren't "required" by the Consumer Rights Act - they're a way of formalising the liability for any faults but are always additional to the CRA rights, not instead of.If you use a dealer it will come with a warranty as required by the Consumer Rights Act - but most dealer will offer slightly more friendly warranty. If they don't - look elsewhere.
Warranties on second hand vans will be governed by the T&C's of the seller, Always read them! If you need warranty work to be done on a second hand caravan always check with your seller about who can do the work and still claim the warranty costs..
Some short warranties are less favourable than CRA rights so effectively worthless.