I was just posting in another thread about how I remade the armrest of my Traveler Guitar to be more comfortable. The one it comes with is super uncomfortable to me, so I redesigned it to be shaped more like a Squier. Images here .
All I really needed was some cardboard, some calipers, and Blender. Though, to get the measurements just so, I had to make a bunch of little virtual rulers (the yellow strips). In CAD, you wouldn't need those since the measurements are described directly in the process of making the part.