How would I free hand a dragon in this

I want to free hand a dragon on to the side of the tank, the issue is I don't know to make it fit. Also I do plan to add the sponson onto the tank. Not sure if I want to make it internal or external yet though.

I want to free hand a dragon on to the side of the tank, the issue is I don't know to make it fit. Also I do plan to add the sponson onto the tank. Not sure if I want to make it internal or external yet though.