The drain tube for the HVAC/EVAP assembly that outlets through the firewall is a poor design. Either due to lack of insulation or a defect in materials the drain tube sweats, builds up moisture in the evap case seal and ultimately drains back into the cab soaking the carpet and resulting in mold. A single trip to the dealer states that drain is operating as it should and the installation of an elbow on the drain was completed to promote the drain to discharge futher away from the foam case seal.