I spent many years linked to the industry as Caravan Manager for one of the then largest finance house /banks.This was and remains a big issue because you buy the van plus sites markup onto which they add a further markup for the pitch (because they spent money on services,base etc and siting)so when you want to sell all that goes plus more.They cannot arrange the finance as the are not the vendor.The NCC is an organisation to represent the manufacturer so no use to you,The BHHPA is likewise a body to represent the site owner,no body exists to represent the 'resident'other that the 'law'.
That said from what you have said whilst not good they have one nothing outside of the law.
Caviat emptor springs to mind,also many sites run on a 'ten year agreement'meaning that after ten years the van has to go meaning you have to sell off site and take a really big hit.
None of this is what you want to hear but that is the way it is.