Newbie here, doing a four tier wedding cake this weekend.  The bride only wants the top tier (6 inch round) to be cake, the rest we decided to do RKT (cheaper than styrafoam).  I've formed the tiers today by packing the RKT really firmly into the cake pans.  I have several "layers" for each tier.  I'm planning to glue them together with a thin layer of buttercream. 

What sort of support system do I need for the cake?  There's a 12, 10 and 8 inch RKT tiers and a 6 inch cake tier.  I am paranoid of it falling apart! 

Also, I have the layers wrapped in saran wrap in the fridge - what's the best way to get them to harden?  I want them to stay hard! 

The cake will be covered in buttercream swirl roses, so very forgiving, lol! 

Are you covering the BC with fondant or just BC? I would support each tier like a real cake. A dowel rod thru the middle will keep it centered.

I'm going to cover it in buttercream and then pipe on the swirl roses. 

I have only learned about the need to center dowel on this site in the last few days.  Makes sooo much sense (would have saved a cake I made a few weeks back, oops!), but I have to admit I'm petrified of trying to ram a dowel through several layers of cake and three cake boards.  How do I do that without smashing the cake?  I just can't picture it going neatly through the cake boards. 

Leah will tell you to use the SPS system! Is it really cheaper to use RTK? Someone posted a link for REALLY cheap Styrofoam dummies recently, then when you count in your hourly rate seems RTK would be more costly!