Mystic used to have a dual-zip lockable kite bag that can be separated into two compartments.
Similar to this...
www.briskites.com.au/index.php?l=product_detail&p=1691 The best part, is that I can separate the bag into two separate bags each weighing no more than 12kgs, with over 4 kites, board, clothes, bars, towels, just about everthing.
But yes, you need to buy more than 20kg worth. Each bag must not weigh more than 32kg (health and safety guidelines from JetStar people I've spoken with).