Hey mercyme are you 100% sure the snow is gonna fly soon? i hoe your rigggggght!!!! First things first, go with the Yakima Lowrider roof rack system. The Yakima Lowider system includes four Lowrider Towers and two cross bars. The Lowrider Towers connect directly to your 2002 Mercedes ML 350 roof rack side rails. You can then connect any of yakima racks snowboard carriers to the Lowrider front and rear cross bars. The 58" cross bars are the recommended length for your Mercedes ML350 rooftop. I like the Yakima FatCat 6 snowboard rack ( actually carriers up to 6 pairs of skis or 4 snowboards and you can mix and match) the best. It has the easist to use release and cling mechanism that won't let you down when it's buuurrrrrrrr cold. Highly suggest a 6 pack of yakima locks too. This way you can use 4 locks to lock the Lowrider towers to your Mercedes ml350 roof rack siderails. and the other 2 locks can be used to lock the snowboards inside the Fat Cat 6 snowboard rack. Another resource for possible snowboard rack suggestions is this
list of mercedes car rack pictures or this
page with mercedes roof rack images.