The hardsided Portercase in its many iterations supports 200 lbs when used as a cart. I used to travel every week with the 18" carryon and sit on it at the Southwest gate. It wheels like a suitcase and then converts to a cart that supports 200 lbs. Some photographer claimed to cart 300 lbs of equipment on his. The suitcase itself is heavy, though. I weighed mine once, and it was 13 lbs. I don't fly Southwest anymore, so the need to sit on my suitcase was eliminated.
Porter Case - /catalog/