I just had this same dilemma as I made a fondant covered cake with ganache underneath. I also had a layer of royal icing on part of the cake too. Many people said do not place in the fridge & others said you have to with the ganache. Living a sub tropical climate I decided to store my cake in the fridge, uncovered and took some advice I read on a forum and placed it under a fan for 10 mins just before serving to dry out any condensation. It worked perfectly – fresh cake, no condensation and even the royal icing layer stayed crunchy. Leaving it uncovered is most important. Once cut I experimented by covering a slice and the icings went sticky!