It's been a while, but I thought it might be nice to update this question. Last summer I've visited japan and found a camping ground at lake Aokiko. I've stayed at the Aokiko camping ground (http://www.aokiko.com/), also home of the "Evergreen outdoor center".
Despite the english name, the staff doesn't speak a word English, I was happy with my pre-translated paper so that I was able to point out that I wanted to stay there for a week.
The camping is very quiet, except for the times when groups of school children visit overnight. Apart from the camping ground, there are also cabins for rent.
The facilities are pretty basic, but ok. You'll have to pay to use the showers. There's a small shop where you can buy some basic stuff (not much food). There's also a device to charge your phone in, but it's all in Japanese, so I couldn't work it out.
The nearest station is the Station of Yanaba. There's also a station closer by called "Yanaba Ski Jomae Station", but as you can guess by the name, it's only in use during winter time. Yanaba doesn't have any shops, the nearest place I found to get groceries is Kitaomachi.
If you're ever in the area and have some time to spare, I would recommend going to Hakuba and taking the rope way up the mountain.