Next time, with the cake on a board that is the same size as the cake, try having the cake sit atop something smaller than it is. When you cover it the fondant will hang down below the bottom of the cake. Then trim it. Smooth it again in a downward motion. A little more fondant will hang below the bottom of the cake. Trim it. Then place it on your presentation board, attaching it with carpet tape or photo mount tape.
That will solve the wrinkling and bunching at the bottom problem.
Hope this makes since. It's easier to show you than tell you