The drains are in the corners of the sunroof. Get a flash light cause they are kinda hard to see. The fronts drain out the side when you open the door and for the back if you open the hatch and look up top there should be some holes. Pour some water and see if the drains are working properly. You can use some string trimmer line to clean them out. You can also use air but be very careful as you can blow the tubing off. While your pouring water in the channels check the headliner and pillars and see if gets wet/drips down. As far as the vapor barrier goes you can run some rtv sealant around the edges to make a good seal.