I have an MXR M222 talkbox that I'm pretty happy with, but when the tube is disconnected the speaker is very exposed:

I'm worried about damage to the speaker, and would like some sort of cap to protect it. When I search for "MXR M222 talkbox cap" or similar I don't find anything. I wonder if it would be possible to make something?

Measuring, the outer diameter [1] is 24mm:

It sticks 10mm up from the plane of the box.

Would 3D printing be the way to go, or are the materials not a good match for a friction fit? Elastic + cloth is another idea. Suggestions?

[1] In case anyone's curious, I also measured the inner diameter while I was at it, and it's 19mm, almost exactly.