I found these excellent cloud brushes. However I only use one of them, used as a brush preset. It makes the absolute, best cloud ever. See what you think.
I use a liberal pressure for the background clouds. And the layering is excellent. If you tap the brush it makes smaller more concentrated clouds. Layering clouds lighter or darker to mimic sunlight or precipitation is effortless. I stamped it with the brush creator's credit.
You can just use a cloud image like it,(b&w), magic erase the sky around it and use the settings Jenn used. She did such a beautiful job with them.
Brian LeBlanc, Fantasy Illustrator.