I throw my chisels and Japanese planes into a bag. I cover the chisels using vinyl tubing sections, but I had not addressed the planes until now.
I made one for each of my small kanna. I was able to get two out of a short length of 2x6 spruce.
For a simple retention mechanism, I used 3/8 flexible vinyl tubing held in position with copper wire (from a short length of Romex).
Here you can see that the tubing tilts inside to press against the dai. I'm hope it works long-term without fuss.
The tubing does lose memory over time but not enough to do anything about it (yet?)