Not had a recent stop over visit to Shell Island but have visited there recently. Not a good experience if im honest. No real reason but some of the people we saw staying there you wouldnt want to leave your van unlocked......i used to spend 6 weeks a year there as a kid so loved the place.
If you like the area then try Parc Isaf near Dyffryn...its a small site, really clean, not too busy unless its the main weeks and the owners are a farming family who look after the site.