I am just a newbie and started with Learning digital mapping techniques only 2 weeks ago.
I noticed that I when I was using the Terraformer in FT3 and added clouds, then when I loaded the file in Wilbur, the clouds were interpreted like altitude maps giving interesting and realistic shapes.
Unfortunately I was unable to edit these shapes to give a map I wanted and then I happened on this tutorial doing exactly what I wanted to do.
First results are good and that's why I would also like to say a loud Thank you.
Really an impressively efficient workflow!

Btw a small comment. As I am not a very proficient GIMP user, I followed the tutorial literally step by step and noticed a confusing explanation in the first part.
It should be :
New layer>White (Clouds 2)
Set mode to difference
Filter>Render>Clouds>Difference Clouds
Set mode to difference (because the previous operation resets the mode to normal)
New from Visible (Difference1)
Then same for Clouds4

So (unless I severely misunderstood something) the Set mode to difference has to be done twice what was not clear from the tutorial