Good evening Rob,

Just forgot to mention that you could always use Google SketchUp. It's free, and extremely easy. The learning process takes less than 4 hours to be honest. It is completely free, there are lots of plugins out there. Many people use it here on the forum (I could think of Boyan, Lee, and many others). Have a look at it. It is very light. It was designed to be easy.

Might be better off trying that before Fusion 360. Then may be you can use F360 for the CAM part.

All the best,