Hello Mick,
Just in case you are not aware of the differences between your statutory rights, guarantees and extended warranties, briefly:
Your statutory rights are unassailable, and under the Sale of Goods act, it is the responsibility of the retailer to ensure the product is fit for purpose and free from defects. The retailer cannot avoid that responsibility, it is the law. If something breaks that shouldn't then within a reasonable time that should be covered by the Sog Act. And as a consequence you would have to return it to the retailer.
This applies to all products (not just caravans) so you can replace references to caravan with any product or vice versa.
There is nothing in law that says you have to have a caravan serviced, but it has to be road worthy and there are certain items that will be classed as consumables which may need professional attention, so servicing is strongly advised and probably necessary. The dealer cannot insist you have the caravan serviced by them. However you may need to prove it was done by a competent person.
The SoG only really covers fundamental failures, and its strength diminishes with age of the appliance. So most caravan manufactures offer a warranty scheme. This is not a legal requirement and it is 'in the gift' of the manufacture, so it can be constrained with special conditions.
Typical conditions include :
Who can service the caravan,
How many miles/months between services
The use to which the caravan is put (i.e. Domestic only)
Not to be towed behind commercial vehicles
the Warranty is not transferable to second purchaser or beyond.
Some manufacture also seek to limit cover on certain items such as exterior plastic mouldings etc
It is fundamentally a contract, and if you break it then the contract can be declared void.
Extended warranties, are not technically warranties, because you make a special payment for them and they are actually an insurance process. Again these can be conditional and subject to strict adherence to the terms of the contract.
So in short if you wish to retain the cover of the manufactures warranty, you must abide by the terms in the contract.