Hi, I am making a 3D replica motorbike cake, I am going to be making the structure using ply wood and wooden dowels. My question is how do I make this structure food safe? Would you use cling film or tin foil and cover in chocolate or is there anything else you would suggest? Thank you.

From what I've seen watching the cake shows on tv I would suggest covering the wood with a coating of ganash or melted chocolate.  (white or whatever color that will not been seen).  Cling film or foil can easily be cut/torn while cutting the cake. 

I've always covered mine with plastic wrap, foil or both.  You do have to be very careful to not include a chunk of foil with the cake slice!