Park Resorts have a couple of sites over here as well. But am sure they will be far from quiet, although saying that the sites are quite big for campers. Will have a think and update the list if we think of any others that are suitable.
There's one called pickpockets, nr newtown if memory serves. Its in the camping and caravanning club book. Only got 6 pitches, toilet and sink and water tap. Nice meadow in forest clearing.
Try Grange farm, They can sort the ferry out for you too. I will be going there a couple of times this year with Grace