go to a hobby or fabric shop and get a roll of 2.5inch wide sticky back Velcro and put on the bottom of the box.its working fine for me.

 

put a sheet of mdf under the carpet and but brackets on the subbox and screw it down, you should even glue the sheet of wood to the trunk floor so the box is totaly secured down (from theifs) and if you wanna go that extra mile get some security screw it screw it down or allen key screws to stop crack heads.