Hello Ian,
I stand by my statements, and I will add comment here to hopefully clarify further.
As far as I am aware, there is no legislation that states that a seller must carryout a PDI on a caravan or any other product.. It follows therefore that a PDI is a service that the seller is offering, and if the offer is accepted they are contracted to do it. If they invoice for it and don't do it, that would be fraud.
PDI's
Who benefits from the PDI? If the caravan manufacture produced and delivered a quality product then a PDI would be unnecessary. So it is a crafty way to get the customer to pay for manufactures inadequacies. It is a very expensive way of trying to manage product quality - it is much better to do right first time. We should also be asking why does the customer have to pay for it?
Warranties.
I suspect you may have made the same basic mistake that many customers make, that is to confuse the the distinction between the customers legal rights under UK legislation, and the gift that is sometimes made of the manufactures warranty. (though in practice the selling price is lifted to cover faults and repairs so it is not actually free) In addition the extended warranties that are sold, are not guarantees but an insurance policy, and many studies by consumer organisations suggest that they are over priced, and are very lucrative for the manufacture and insurance companies.
All traders/sellers/dealers are obliged under the consumer rights acts, to ensure that the product they sell is fit for purpose, and of merchantable quality. If a product fails in any of those regards then the customer has an inalienable right to satisfaction against the seller. Only the seller and customer are legally obliged in this remedy. The manufacture has no jurisdiction in this area unless they are the seller.
Manufactures warranties are a gift from the manufacture, and they can define and limit who is the beneficiary. They rely on the manufacture having established contractual arrangements with a network of dealers/traders/sellers who agree to undertake warranty work on the manufactures products. The dealers may agree to undertake work on caravan not belonging to one of their own customers, subject to the terms of the contract with the manufacture. This is the process you describe. However the customer can insist on their legal rights provided they bought the van from that dealer.
If a customer had evidence that their complaint was being deliberately held back by their supplier pending the manufactures input, then they would have a possible case of breach of contract against the seller.
100% 80% 85% 7% 10% figures?
Some drivers are limited to towing a trailer that does not exceed the MAM of the car effectively a 100% figure, but apart from that it is my understanding that are no statutory regulations that define a required % of nose weight, or mass ratios between the tug and the trailer. The regulations do require that the driver ensures the vehicle (and trailer) is in a road worth condition, and that includes that none of the manufactures stipulated limits for load and masses are exceeded.
If any limit is exceeded, then the outfit is not in a legally road worth condition. Equally if an outfit is uncontrollable (unstable) it is automatically Unsafe and therefore illegal.
Notwithstanding the above, many of the suggested % guidelines actually make good sense, but it is important to realise that simply keeping to a specific ratio or limit does not ensure a safe outfit. Other important factors must also be satisfied to maximise the potential safety margins such as balanced loading, tyres etc.
Site densities
I do not know if there any national regulations that define the maximum density and or minimum distance between caravans, but such issues should have been specified on the planning proposal for the business and submitted to the local planning office. Again I am aware there are certain dimensional standards suggested by the Caravan Organisations, but these are only guidelines.
So most areas of caravaning are subject to regulations or controls of some type, but in the wider context of trailers as a genre. It would be difficult for the legislators to enact specific regulations for Caravans, as defining what constitutes a caravan and to differentiate them form from other types of trailers would be problematical.
I still think that the relevant controls are there, but there is widespread ignorance of the detail of the legislation, not only by caravanners but by enforcement authorities and other towers.