GAS Dryers require solid Metal (not flexible silver foil type) exhaust tubes, due to the HEAT a Gas burner puts out. 120/240 dryers also request same venting but you can get by with standard accordion type dryer hoses. The air venting is to make sure you have enough intake air INSIDE the home to keep from exhausting the air inside the dwelling and have enough volume of air for the usage of the Dryer Gas Burner. Since it specifies Mobile Home, there must be a history of Mobile homes being more airtight than standard stick homes. Doug