I went to Empangeni (south africa) to bake cakes for my 2 grandchildren. Empangeni has a tropical climate, and the humidity got very high. The fondant wouldn't even dry out! Not even royal icing dried. One of the cakes was a castle cake, so the towers (however properly anchored), started falling. We even put the cakes in a room with aircon on very low. So I had to fix this towers, and because the royal icing is not doing its job, i used melted marshmellows instead. That worked well. I agree, that climate, and that kind of humidity, is not suitable for either fondant or royal icing.