You mean just cardboard and tape isn't trustworthy?
I've made a sheath the way I described above ...
Hmm! It seems you've had better luck than I have. I've had knife points penetrate tape-and-cardboard in soft-sided checked luggage. But it could be my lousy construction skills
. I'll give your method another look.
...cardboard from tetra-pack box of milk ought to be waterproof
Good idea.