Living here in France, it does get quite hot in the summer, and I have used many a display cake in the heat. The only thing you need to worry about is moisture and direct sunlight, otherwise I have found that the fondant takes the heat okay. I usually make mine and let the cakes set for a good few days so that the fondant sets hard, and the I decorate it and have had no problem.
One major thing you will need to secure any large flowers with glue, as you cant’t use any white chocolate.
Good luck.
gateaux de mandy
