The Burrow, the Forest of Dean, and Everything in Between (but not Hogwarts)
That's right—for the first time in the whole series, Harry is not back at Hogwarts when the school year begins. It's gotten too dangerous for Harry and his friends to be seen out and about (and they have a secret mission), so they decide to go under the radar.
To avoid capture, the kids move around from place to place quite a bit. At first, they hang out in 12 Grimmauld Place (the Order's headquarters), since it's got all kinds of magical protections.
However, when that sanctuary gets breached, they have to start camping at various locations…none of which are as warm and cozy as the Burrow (Ron's house) or Hogwarts. The tent they use is probably nicer than your average camping gear (and larger), but it's certainly not homey—it's no wonder Ron (and then Harry and Hermione) gets grumpy.
Of course, Harry has bigger problems than an undecorated, slightly depressing tent—but nonetheless, we kind of hope that he finds his way to better digs soon. Maybe he can make that priority #2 after the whole "Defeating all the evil in the world" mission.