I never transport a fully assembled cake. I’m too scared of the risks (learnt the hard way in my early days of decorating) … so I organise to get there super early and take my time assembling on site if possible. (This might not be what you want to do though, reading your write up Julia, but I’m paranoid hahaha so I do) the most I will do is 2 tiers together so for 5 tiers, I may do 2 tiers, 2 tiers then one tier… all separately boxed and carefully packed into the car… if flowers are involved, I assemble them on site, to minimise risk of breakage. I pre pack them carefully with them well fixed into a dummy cake, then i use soft baby tissues to wrap around each sugar flower as light, soft and hold the flowers gently with no rattling around over bumps etc. These are boxed as well, ensuring space around where petals are.
I also have all the cakes pre-dowelled so ready to stack on site.
i also place a non-stick mat under each cake in its box to ensure no sliding.
You must never limit your challenges, instead you must challenge your limits