When you make a tiered cake with dummy, do you use cake boards under the dummy?
I just use buttercream frosting not fondant.
No need for boards or supports, just stack the dummies and decorate them. Attach them together with tape in between them, or royal icing or melted chocolate or staples or however you want to do it.
I would definitely use a board under the stacked cakes, because it would look more like a real cake - you could decorate the boards edge with ribbon to make it look more believable but the most important point is moveability. without a board you have nothing to hold onto when moving the cake and may leave marks in the icing.
Are you talking about a board under the base cake? Yeah, you need to carry it around so put it on a base board.