Hi @Margreet,
Is your box placed indoor or outdoor? What is the max humidity that you would recommend?
If I use an IP66 box, like https://www.se.com/nl/nl/product/NSYCRN64200P/spacial-crn-deur-met-montageplaat-600x400x200mm-ip66-ik10-ral7035/, and only place a Multiplus II 3kVA 230V inside, is it okay not to have ventilation?