Dowelling a barrel cake

Hi all. Please can someone advise me. I have been asked to do a barrel cake which will consist of 3 × 1.5″ lemon sponges for the bottom and 3 × 1.5″ vanilla sponges for the top. They will all be 8" round. I need to know the best way to dowel it ie should I dowel the bottom layer (the vanilla will be on a board) and should I then put one large dowel through them all. I am worried as they will be transporting the cake about 50 miles. Thanks so much. Sharon xx