I too live where it is very warm and humid during the summer months. It can reach into the 90*f or 32*c and have 80% humidity almost every day. It can be very challenging trying to stack a wedding cake! I found this recipe here on cd and have used it every since I’ve found it. It is for American Buttercream which can be covered with fondant also. I had to adjust the ingredients to suit my climate. I hope this helps! http://cakesdecor.com/entries/169-how-to-get-smooth-butter-cream-that-stands-up-to-heat-and-humidity
Psalm 127:1 Unless the LORD builds the house, the builders labor in vain.
