Hello, I have been asked to do a princess castle cake next month. I have only made one other one before and I thought everything was fine until I had to transport it. The fondant pillars pulled away from the cake and I had to pull over to fix them. I am still kinda new at this, so need some advice on how to best attach the pillars to cake and board to prevent this. Also this will most likely be 3 tiers high, a first for me...do I assemble then deliver or deliver then assemble? Any other tips you have for such a big cake would be a great help!!
Thank you!

Deliver THEN assemble. Stack your tiers with the proper support and and then decorate as much as you can before delivering. Wait till you arrive at your destination before attaching any pieces like the pillars or figures that could move during transport. You can use gum glue to attach decorations.

I made a castle with strong tall towers that lasted a long bumpy car journey in the same way I did the tower in this (there's a guide as the last pic):
http://cakecentral.com/gallery/2052120/rapunzels-tower-theme-cake-guide
Hope it helps