The preposition ''в'' can use both the accusative and prepositional case: the first one to indicate direction and the second one to indicate location. So, in your example: собирать в хранилища (accusative) -- to collect into storage facilities, while храниться в хранилищах (prepositional) -- to be stored in storage facilities.
Another example: ехать в город -- to go to the city; жить в городе -- to live in the city