The Collaborative International Dictionary of English v.0.48:

Camper \Camp"er\, n.
   1. One who lodges temporarily in a hut or camp, especially
      who sleeps in a wilderness for recreation.
      [1913 Webster]

   2. A person who stays at a summer camp or day camp.
      [PJC]

   3. A vehicle, such as a small truck, or a pickup truck with a
      hood over the back, equipped for convenience while camping
      out.
      [PJC]

   happy camper a person who is pleased with the situation in
      which s/he finds him/herself. Often used ironically or in
      understatement, especially in the negative; as, the
      passengers left behind on the island were not a bunch of
      happy campers.
      [PJC] Campestral