Hi Zoe!
First, make sure that the entire stacked cake is built on a very strong cake board. If this board is flimsy, you will risk the dowels moving in the sponge cake when you lift the finished cake for transportation.
Second, dowel the cake as Callicious Cakes described: 1 dowel in center of sponge cake, 4 placed around this central dowel about 3" from the center. Wooden dowels are perfect. Also ensure that they are well spaced from each other to take the weight above.
Third, ensure that the foil cake board holding the fruitcake is also very strong. Use two or three foil cake boards if you have access to only the thinner ones. Glue gun or tape the foil boards all together. This will prevent the dowels below from pushing up into a single cake board and possibly cracking the heavier fruitcake above. Check the diameter of foil boards you will need to fit under the fruitcake ahead of time just in case they need to be cut slightly smaller.
This should do it. Built a little like a fortress.
Because you are being cautious, I believe you will do well! Good luck!
Beverley Way, http://www.beverleywaycollection.com, https://www.facebook.com/BeverleyWayCollection
