I don't think there is any official hook-ups on Expo, at least I didn't see any the one time I stayed there a few years back.
However, several enterprising (and presumably knowledgable) people seemed to hack into a supply - there were so many cables coming out of this unofficial connection it looked positively dangerous.
Apart from the concrete ground, I quite liked Expo - very close to the main circuit entrance, and with a bar right outside the site entrance. Also very useful in the odd wet years if you can bag a space under the cattle sheds.
Del