Thanks for the info Chip and Marco, much appreciated. The cannon looks great! This brings me on another possible reason to go for 3D Coat: how good is its capacity to auto-generate a hollow model with just the right wall thickness?

In ZBrush you can use the Dynamesh Shell function to create a wall thickness based on voxels, but in practice the Shapeways 3D print auto-check still finds weak areas with insufficient wall thickness, so ZBrush Dynamesh Shell isn't the one-stop solution I'm looking for.