Originally Posted by Chris Mason
You really don't need an adjustable box. Just get a box, or have one made, and then buy some cheap rubber floor pads and cut them into squares that match your box and use them to adjust the height as needed.
+1. Get a 12" box and stack on top of it. Good one on the floor pads--I use bumper plates. Though the adjustable box would be sweet if you have the $ (like the others, more important items on the top of the list).