Winter Cover

For those of you with the galvanized garden “boxes” that have the rounded ends, how do you cover it to make the crop last longer or through winter?

Hi Shereeka, welcome to this board.
I'm trying to imagine the type of boxes you are referring to.
Raised garden beds or window boxes?
The volume of the container would make a huge difference to the answer.
Do you have a photo or can you reply with a link to an online image, say on google please?
Also how cold are you expecting your area to get?