Hi Dan,
Was up chav land - sorry, Haggerston - coupla weeks ago and though I drove, a lovely back road route...
200yds north out of the site entrance turn left and follow twisty but decent back road route to Cornhill (Coldstream), then follow the road skirting the south side of the river to Kelso then back across to Haggerston.
You'd be best to google map it and its around 50 miles but could shorten it by just doing cornhill and back or Kelso and back.