Use car carpet, you can find it at your local car mega-store. Its thinner and easier to work with.
When I did car stereo installs in a previous life...
Wrap the ends first. Use 3M Super 77 glue to glue the flat part of the box, then fold the sides over just like wrapping a christmas present. Cut the corners at a 45 degree angle across the intersection of the two sides. Fold down and glue.
Wrap the outside of the box, using the spray glue, being careful to blend the nap at the edges with the nap on the sides. Do it right, and you'll never notice the joint.
A few stragetically placed staples can make life easier, also. Just make sure you cover the staples with the final wrap.
A clean, stiff, brush can be used to join the naps where seams are visible.