Leave the tank in the car. The neck has to go through the quarter panel on the Duster. It will go in from the outside into the trunk then into the tank. There is a flange that the retaining screws go into the quarter panel. The gas cap covers all of this when you put it in. Just use some penetrant on the grommet. Don't forget once the neck is partially through to in the truck seal. But no taking the tank out will not work on a Dart Sport/ Duster or Demon.
Thank you, Ken