If you glance around a race site you'll see that sled dog trucks are as varied as their owners but they have many common features. Dog trucks are equipped with separate compartments built on the truck itself or on a trailer. The boxes are kept relatively small so the dog's body heat will keep the box and the dog warm, but yet large enough that the dog can travel in comfort. Sled dog boxes are well ventilated so the dogs get fresh air and stay dry. The humidity from the dog's breath would make the box a damp and then cold place if it is not allowed to escape through vents or the door.
Most boxes have a large opening covered with some form of metal grating.
When the temperatures are colder than what the dog normally experiences a portion of the metal grating or other opening may be partially covered to conserve heat, yet still allow humidity to escape. Mushers put a variety of materials in the boxes for bedding. The most common bedding is fresh straw. Straw provides padding and insulation. It must be changed regularly so it does not become wet, molded or soiled.