I found that a great way of quickly modelling up casings was to use a rigid foam former. Using some trashed styrofoam, a bandsaw and a belt sander one can make a former in minutes. At first I was draping terracotta directly onto the formers, but encountered cracking as you can see in the pictures. Putting a damp newspaper seems to solve this, and having a complete 3D sketch in 20 minutes is great thing…..