We went to a rally some years ago at Rockingham Castle, only a small event with a handful of engines and it struck me at the time how good this venue would be for a larger rally.
Some pics I took at that event:
http://www.steamscenes.org.uk/events...-castle-steam/
I'd agree that the venue is as good if not better than existing Belvoir Castle site and unfortunately that old mid-May date was often wet (although they did have several very warm weekends).
One to look forward to.