How do I stack dummy cakes (4 tiers) together? Do I use thin cards for each cake? or do I dowel the cake like a real cake? What do I use to stick them together as I will be delivering the cake with decorations on.   Please help! Your help is appreciated.

Thank you.

You don't have to put them on boards, and you don't need to dowel. You can just use royal icing to stick them together - leave enough time for it to dry before you move the cake into your car for delivery.
 

Agree with Dayti. You could use a dowel or skewer if you wanted to, but not really necessary. 

I use royal icing or low temp hot glue.  Either works very well.

Rae