Hi, I am doing a barrel cake in buttercream, what's the best Way to transport it to prevent it cracking? Any tips will be appreciated!

If you put the correct support system inside it you shouldn't have any problems. What were you planning on doing?

It's actually a pill bottle covered in bc. 7" I will be glueing a dowel onto a mdf board and then threading the cakes! Also is it best to "thread" the cakes while they are cold or room temperature?
I will be using bible tea straw also!

The most important this is that you treat it like a 2 tier cake structurally. At the middle point there needs to be a board and dowels underneath and then you can ice it up as one.