@mahgnillig, I wouldn't worry about the rust unless it is red and "blooming". Black discoloration and flat red rust will not affect the skis' performance, and the red stuff will definitely wear off within a few runs, black stuff after several days on the hill. Red rust in areas where there is little contact with the snow, of course, should be smoothed out down to the black stuff, as it can grow, but I would leave the black stuff and stains alone. Trying to get it off may do more damage to the edge than the rust itself; better to wait until the whole edge is re-sharpened.
That said, you could try a coat of liquid or paste universal wax like Swix F4. I have also seen people recommend Zardoz NotWax. I couldn't tell you how effective these are because I carry my skis inside the car, more because the roads kick up a lot of dirt around here. I also bring the skis into the motel room every night and dry them out;
in fact, this might be the key for you, since a sure-fire way to get rust on edges is to leave wet skis in the car overnight. (You can bet same applies to the internals of the bindings, although there is a lot of grease in there.) Even if the skis are dry, the air can get pretty moist overnight, and that is a bigger threat to steel than droplets of water. (Remember experiments of leaving nails half in water? They rust the most where air and water meet and above, where there is moisture
and air.)
Incidentally--for dirt-scratch prevention, and not for rust prevention--when I have to use roof racks, I put little plastic bags over the tips. The kind that newspapers are delivered in works well, and are long enough to be held down where the skis are held together.
I suspect tape by itself won't be that useful, as the water can seep in and actually stay on longer. This can also happen with boxes and bags, so make sure they are dry. If you are wrapping your skis in bags, I would definitely not leave them in the car overnight;
wet bags will promote rust for sure.
