ok me and my cuzen in stall them for kids at our school because there to rich to do it for them selfs. Is your box padded? if not do that. Also you might want to put a bar that gos right across the mid box... it looks cool and it helps so the box doent move.
Me and him where thinking about this and it could be some thing lose in the trunk ...Like a wireing box for your lights.. or wires that are taping the trunk. If not that Look under the back bumper make shur every thing is where it should be. If you have all that checked off for a yes every thing is fine.... I dont know What it could be
