I assume you're decorating dummie cakes. Do them early so they harden up a little. Should be no problem. If that fondant is going to melt, it will be too unbearably hot for patrons.
Don't you have dummy displays in your bakery? I'm not quite sure why you are worring. These shows are a drop kick. Bring a few dummies. Set your display and viola. Make sure you have different size risers to elevate the cakes. The shows are usually crowded. I have only done a couple of small private shows years ago. I have attended many and have been asked advice on displays. The best booth I worked on was when we stacked two tables in the rear of the booth and put the biggest cake on top.
The cake bottom was at about 7 ft with another 4 ft. of cake. We put some spot lights on it. It was a stand out ,since all the others were lower and it was so crowded because the cake venders gave samples. It's like feeding anamals at the zoo. The reasonI refuse to do them.
Make sure you have all your permits, licenses, and such, available. You might get a visit from the health deptartment.
PS. The most important thing is you brochures, directions, and feeding sizes. I would refuse to have any sort of consultations with customers. Just set them up for tastings. There will be many people who just waste your time yadda yadda and don't even need a cake. Sometimes the competition will be shopping you. That's what I do sometimes.
Here, the State law prohibits preparing any food at home for the public. So if I'm available, I will go around the show and give the bakers that are flying under the radar a hard time. One time I went up to a booth of a known home baker. I listened to her shpeel until she told me to go with my fiancee to a consultation/tasting at Frosted Art Bakery or Panini Bakery (my bakery). Get everything worked up and designed. Bring the contract to me and I'll beat their price because I don't have the overhead and I don't have to pay for advertising. We had never spent money on advertising and come that Monday I decided to drop a dime on her. She was 86'd and slapped with a substancial fine. I didn't feel bad though, her husband was one of the biggest Cosmetic Dentist around and they live in a mansion.