Carrying skis and snowboards inside your trunk equals dull edges and a snowy mess after a gnarly day of shredding pow pow. We should throw a bro in there somewhere. At any rate, as in most sports, the rule of the day is that people go inside the vehicle, gear goes outside, or else everyone gets a damp bum in the winter and a sandy one in the summer.
You can carry your skis and snowboards on mounts that clip to factory, round, square or aero bars. These clamp down on the equipment in question with a soft rubber gasket that holds things where you want them (i.e., on the top of the car). Another option using a cargo box, so that your gear stays out of the corrosive, salty spray that is so common in the winter.