I purchased a 2007 Frontier Crew Cab on eBay in September of last year. I came with an OEM Tonneau cover. I haven't had it on but decided to try it out for a while. It was pretty easy to put together but I can't figure out what holds it to the bed. It has 4 brackets (2 on each side) with holes in them but nothing I can see on the rail system that they attach to. Maybe I am missing some parts. Can anyone help me out, maybe with a picture or something to illustrate?