I decorate cakes for the fair every summer, and want to do a Baseball Cap cake. The cakes I do a dummy cakes, so I will be putting the fondant right on the pan. I don't know how it will do in the KY summer heat. I have only ever done royal icing and that has given me problems in the past.
I think if you do it with some time to dry ...maybe the least a couple of weeks you wouldn't have a problem. I live in FLorida and it gets very hot. The dummies are made in styrofoam and fondant and they handle the heat with no problem. Of course they are usually made with some time of anticipation.
I usually do my cake a week or 2 before the fair b/c it needed time to set. Also I have had my dogs get into it.
I never done mine in RI so i dont know about that. But I know RI icing can be a problem if it gets in touch with some grease..