The roof line of the xterra is not a flat line, it is lower over the Driver/passenger seats...so you probably won't be able to mount the entire rack unless your cover isn't flat or you fab something up. So I think you would be able to mount up the back half of the rack, I'm not at my truck but I bet it is under 6 feet. You may have to cut the front off the rack I can't remember if the rails are one piece. Good luck