This is the storage space underneath my stairs at the front door. Looking at the photo on the left, the left wall is the back wall to my HT system components.
The sub drivers will sit vertically in between the last two studs as pointed out on the right. They will be mounted on a 2.25" thick MDF baffle. The baffle will then be mounted to the two studs.
The total space is greater than 160 cu.ft. Keeping in that there will not be too much junk stored in there.