I finished my strip light (see part one of the documentation.)
The material I used for the diffusor came from an old shower curtain, which was all white and made of polyester, and in look and feel it’s very similar to the material used in commercial light modifiers. I put some Velcro strips on and then painted the whole thing.
The only thing I will probably do at some point is to replace the cardboard bottom with a piece of wood. Other than that, it works great and was well worth the effort!