In principle, the packaging has lost its Union status and must be declared in order for goods to regain Union status.
How it works:
Please note! In your booking with the ferry operator, clearly state that you are transporting empty packaging. Also make sure that you comply with the Customs regulations: (in Dutch): https://www.getreadyforbrexit.eu/wp-content/uploads/2020/10/2020-09-28-Memo-ODB-terugkerende-emballage-en-verpakkingen1.pdf