If the sub is in a the box it came mounted in it might not be as good if you take it out. Speaker cabs are supposed to be designed to have a specific volume of air in relation to the speaker, there are all sorts of calculations relating to vented and unvented sub boxes. If the sub was cheap then the cab may just be designed on looks, but I would suggest that it might be best to cut a hole and mount the whole box behind it, leaving the sub in the original container.