If this had been pure marine/transport insurance, I would have understood
en charge as “(goods) in transit/being transported”:
Charge: …ce que porte ou peut porter un animal, un véhicule, un bâtiment… La charge d'un navire. Sa cargaison. Prendre charge (d'un navire) : être chargé. (
https://www.cnrtl.fr/definition/charge under II A 1 a). See also
Le Grand Robert de la langue française:
Rompre charge : décharger des marchandises en vue d'un transport par une autre voie. Similarly,
chargeur/rupture de charge, i.e. “shipper/transport being interrupted”.
I can’t find any example of
espaces de stockage en charge and I'm wondering whether this could be read as
espaces de stockage [des marchandises] en charge. Can't find that either but bearing the above definitions in mind, your
espace de stockage en charge could possibly mean “stocking space (warehouse?) for goods being transported/in transit”, said goods first leaving the consignor’s premises to be stored centrally at the shippers' (main) place, then being dispatched and stored locally (different consignees?).