[morzh]

The felt stripping I thought of proved to be very thin and narrower than I though.
I found felt weather stripping but this also was very thin and very wide.

So I found regular rubber foam weather stripping that was very close in both width and thickness, and it is self-adhesive so no gluing headache.....and the compression degree is about adequate, so it sticks out enough and gets some compression when the speaker is installed.