if u want u drill piolet holes on the corners of the box, then thru the floor (piolet holes, not large drill bits). go into your fancy toolbox and look for the smallest screw u have, ajust your piolet hole in the truck floor accordingly and then drill into the box (without ajusting it to the screw size). This should work, u can use a fairly short screw ONLY if the box isent shfting a hell of alot
Get a new solid rear window lol . i think thats what im going to have to do . mine rattles at low volumes and high volumes . only thing you may be able to do is add some weather stripping in the groove and see if that helps .