In most cases leaving your car at the campervan depot is not an option. This does vary and will depend on the policies of the your chosen rental company. Where a supplier offers this options it may be free or subject to a fee. Contact the campervan branch to confirm parking options prior to your pick up date.
You may also want to consider other options, such as public parking or long-term parking facilities, if leaving your own vehicle at the rental location is not an option.