You don't need to put rails on your car. If your car has 4 doors all you'll need is Thule's 400XT Aero Foot Kit with the correct fit kit for your car, as well as the load bars. You can definetly put 2 kayaks on the car. Either the Thule stacker or the Hullaport Pro would be my reccomendations. The Stacker will offer the option to carry more boats and it's a better deal. You will only need one stacker regardless of how many boats you'll need to carry. A 50" load bar is reccomended for your car. I'd got with the next size up which I believe is a 58" it could make all the difference on what you can put on top later on.I have a sentra as well...you can put four ww kayaks with 58" cross bars...I don't even have a stacker--just talk to someone who knows how to use straps well, it'll save you 100 bucks...