You could consider getting good at MeshMixer and create organic shapes that way. Just saying. I do parametric CAD and I'd have a devil of time making nice organic features.
However, consider layer adhesion as your enemy when you have a fighting fish on. As you so correctly point out, you want the line going through the body, not depend on the plastic to hold your catch on the line! Be careful with kinks in the through-hole you need. MeshMixer does rudimentary merge functions and solids to manipulate.
I don't know who is pushing CAD seats for free these days. I pay out the ears for mine.