If all you are going for is a loud box, don't bother with the box around the box idea...in my opinion this won't accomplish anything more than a well sealed box.
To get loud, go ported. Someone around here will help you with a design I am sure, and it will make a huge difference over a sealed enclosure assuming both are built to the sub's likeings (sp?). Stick around for a little while and ask some questions, you will learn a lot