the photo shows that a little was cut off the bottom to stabilize it, but if you don't want to do that, maybe once the cake has been cover you can use royal icing underneath it, or create little legs with skewers on either side and secure with royal icing. good luck, can't wait to see the pictures
AIs that ALL cake? If so, would you mind sharing how you got the cake stabilized on top of the bass drum? And what did you use for a stand for the others?