In cases like these, I always find, it helps to think about the specific objects involved and how they work. You already seem to be thinking along those lines, which is good.
Firstly, you want to use a word which suits the specific objects involved. Are these cargo holds and covers on a boat or a ship?
Secondly, in this instance you want a word which indicates how the covers move. Therefore a word like "on" doesn't work in this sense, because it describes an object in a particular place. It doesn't imply any movement, for example; "The book was on the shelf.", "The dog was on the path.", and even, "The car was on the road.", which by itself, doesn't tell you whether the car was parked or moving.
So, if this is a boat or ship, are the covers thrown over the cargo holds or do they slide over them? Both indicate movement, but what type of movement is right in this scenario?
With those ideas in mind, would you like to have another go? (Please also let me know whether the setting is on a boat, ship, or something else as this will help me to know if you have chosen a version that works).
Interested in Language