One problem related to auxillary tank has been reported for the 2004 Chevrolet Trailblazer. The most recently reported issues are listed below.
Tank is subject to cracking causing rough idle vehicle speed surges and gas vapors in the vehicle and around the vehicle. Vehicle will fail emissions. Manufacture recall was put out but vehicle has to be made at a certain faculty and mine wasn't, but has the same problem as the recalled cars.