How is the hobo camp described in Fahrenheit 451?

The hobo camp that Montag finds is simply a cleared spot by the railroad tracks where the men have made a fire. They are transitory, moving around to avoid detection, so they carry their gear with them and don't remain in any one spot for too long. Montag focuses on the campfire, which is different than fire in his experience; the fire is warming the men instead of burning them.

There was a silence gathered all about that fire and the silence was in the men's faces, and time was there, time enough to sit by this rusting track under the trees, and look at the world and turn it over with the eyes, as if it were held to the centre of the bonfire, a piece of steel these men were all shaping.
(Bradbury, Fahrenheit 451, Google Books)

They also have a portable TV, which they use to watch Montag's chase. Montag, bred of the city, finds himself comfortable and even happy in their company; he has no comprehension of this sort of life, but in its simplicity he finds something he lacked in the city. Once the city has been destroyed, they pack up and walk back towards the city, to help survivors and try to rebuild civilization.

In Fahrenheit 451, who inhabits the hobo camps?

After escaping the city, Montag floats down the river and eventually comes ashore. Seeing a fire in the distance, he finds that his reaction is mixed; he knows fire as a destructive force, but this fire seems to draw him, as if welcoming. He discovers that it is a "hobo camp," the sort that is derided by the people of the city; the inhabitants are educated readers, devoted to the cause of memorizing books and spreading their knowledge:

"This is Fred Clement, former occupant of the Thomas Hardy chair at Cambridge... This other is Dr. Simmons from U.C.L.A., a specialist in Ortega y Gasset; Professor West here did quite a bit for ethics... Reverend Padover here gave a few lectures thirty years ago... Myself: I wrote a book called The Fingers in the Glove; the Proper Relationship between the Individualand Society..."
(Bradbury, Fahrenheit 451, Google Books)

Each of the men is a reader, devoted to the knowledge in books and the worth of individual opinion. Because they memorize books and then destroy them, the content of the books cannot be destroyed unless they themselves are killed, and no one can prove that they know books by heart. Montag, after watching the city's destruction, decides to join with them; they have techniques that will draw the books he read from his subconscious, so he can recite them and help them bring books back to the world.