Hi Jacky, I guess my last answer got lost while I attempted to send it.
Anyway, I did follow your instructions as good as I could, and I did manage to set up the hemispheres with cloud textures applied on them.
Now, I was able to import them, but the result did not look very… convincing. 
In fact, the imported sphere is being treated just like any other prop, and my panner-based materials don’t look too good either.
Could you by any chance be talked into elaborating about this?
The thing for me is, that after three years, for most other topics there is a decent-enough
coverage on youtube, but as soon as it gets to overcast skies… the documentation is slim,
to say the least using the friendliest of terms.
Could you help out here?