The C & CC site at Chertsey is open all year. A pleasant site on the banks of the Thames, and surprisingly peaceful. About 20 mins drive from Legoland. Approx 10 mins walk from Sainsbury's and 15 mins walk from the BR station on the Waterloo line.
I would also go with the C&CC site at Chertsey. Good rail links there both ways, and you are also near to Thorpe Park if you fancy a theme park as well.