once I have put together a triple tier cake, how would I transfer it to the party venue? Do I just find a clean cardboard box and put it in the centre? Nothing to stop it moving around in the car? Do I put a plastic bag over the cake?

I usually make sure I have a center dowel in the cake to stabilize the layers. If I am delivering it I do not box the cake I just set it on some non skid shelving (that I buy at a local store) and transport it that way.

First use SPS. That center dowel is false security. Set the cake board on non-skid mat. Box or not, your choice.