Thanks for the comments, guys. No .tgc for now, because the clouds are pretty simple. Just a few things I've found about making these kinds of clouds:
Make them really thick (2500m or thicker)
Have a big scale range on the noise (lots of octaves)
Have a fair amount of roughness (~2) to get that smaller detail
They don't need to be too dense, but pumping up the edge sharpness helps enhance the detail as well.
Hope that helps
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