If you leave your team to go nap for 2 hours you will fail your whole team. you will most likely get 20 mins rotations for sleep at your post on the field in your gear as the enemy could attack at any time.
get good boots since you'll be on your feet all day and kneepads as your knees will take a beating without them. comfortable eye pro, somthing that isnt too tight on your face and doesnt fog up since you will also be in these all day. Hydration, Hydration, and some more Hydration. dont think that your 3l cammel back is going to be enough water for 18hrs bring extra water to fill it up when back at cp or reloading station.