We stayed there in January this year. We nipped in to the tourist info in avebury, and they gave us a list of sites, but only Blacklands was open. I've chucked the list away, but I seem to remember one was in a Forestry Commission area, and sounded ok.

Most normal people don't camp in January, so the TIC thought we were mad, but they might be worth ringing and seeing what they can recommend.

sam