I have also tried quilling clouds for this one and have used grey, blue and white to give depth to the clouds.
For the water I have just used torn strips the same as described in Tree & Water. The addition of white gives it a beautiful effect.
I am unable to give a step by step description on how it is done as I change my method and shapes from scene to scene and can't quite tell you what I did once it is done, but what I can tell you is that I have not quilled any basic shapes for this project except for the trees in the horizon for which I have used beehive quilling like I did for Flower Fields and Quilled Tree. Most of the others are hand folded or rolled.
When an idea hits me I just draw the element like for example the tree canopy on a rough sheet and then take a few strips and follow my idea and see how it looks from a distance. If I do like it I will use that idea in the scene. Further, I would use different basic shapes for each tree so that the dissimilarity is clear.
Would love to know what you think as always as you are my inspiration.