If cracks appear just keep moist and keep smoothing.

I put a thick layer of stucco on the base over rocks to help with drainage.

I started on the front and worked my way left. I kept the walls moist before applying the stucco, then when the stucco started to dry i would go back over it with a damp sponge and continue to smoothe out.

Now the process of keeping the rain from washing the mud walls. I decided to use stucco because it's easy to work with and provides a nice smooth hard shell. To keep the color natural I mixed in red clay and it gave it a sandy shade.