There aren't any premade boxes you can buy as far as I'm aware, but you should look up the false floor threads made here by the user fourthmeal. From my understanding, the 2005 and up E/M/T have a large plastic spacer that makes up the cargo floor. Removing that plastic space and building your own floor gives you space for a subwoofer box and amp storage. In hybrid models, this is where the battery would go. In older models like mine, the spare tire is stored under that floor. In your Escape, the spare tire is under the vehicle (again, probably to make room for a battery on the hybrid models).
So, remove the carpet and plastic floor from your cargo area and see how much space that gives you.