Check to see that the opening in the roof is large enough, if not cut it to fit. I found a fine metal blade made the smoothest cut, and I sanded it a little. If headroom is an issue, you can also raise it up a little by building up the outside roof a little, and it also gives something to screw into. If you have wires there already, it should hook up easily. If you don't have the power there, a stiff wire can be used to fish it down behind the carpet to hind it.
Good luck, and pictures if you need help.