I made a tiered dummy cake for a photo shoot. One dummy was smeared with crisco, the other buttercream. BOTH made the fondant wrinkly and bumpy, despite the fact that the fondant was smooth and beautiful on the counter! The edges were cracked and dry looking, etc. I used satin ice, about 1/4" thick, just like on my real cakes. I don't usually make dummies and this has never happened to me on a cake. Troubleshooting ideas?
On dummy cakes, I use a spray bottle to lightly spray them with water before placing the fondant over them. With dummies, you don't need to have a layer of buttercream or Crisco.
Also, did you take sandpaper and sand down the top edges of the dummy before fondanting them? Otherwise, the edges are too sharp and your fondant will crack and tear.