We tend to leave ours out without dust protection, so we’re probably not the best people to ask. One tip, though. If you store the AxiDraw with the arm fully right and forward, the cable guides will be at their flattest, which makes the requirements for a cover less demanding.
You might consider asking in the drawingbots discord; there are quite a lot of AxiDraw users there: https://discordapp.com/invite/XHP3dBg
