It's probably easier to commute into Edinburgh for the festival than it ever was - lots of places near the Borders Railway route, and the night bus network goes way out of town so if you want to get back to Bonnyrigg at 3am you can do it. In my village there's the Lothianbridge campsite - 10 minutes walk from the Newtongrange railway station, about a minute's walk from the no. 29 bus stop and five minutes from the nearest night bus stop.