Is actually legal.

Motorists in the United States, as well as some Canadian Provinces, are allowed to operate less-than-truckload b-train configurations (think Truck pulling Travel Trailer pulling Boat). These configurations are not allowed to pass into British Columbia however, and typically the mid-trailer must by a 5th wheel configuration or have a minimum number of axles. Mileage may vary (pun) and you should always check with your local motorvehicle department before planning anything that may be regarded as highway insanity.

Side Note: The longest Bumper Train in the world is the Class K, or Body Plus 6, which is used in mining operations in austraila. They are capable of hauling up to 460 t.