This method uses a "stoned" terrain objects to create the puffs of the cumulonimbus clouds. I have found out that Vue can't render fuzzy materials on terrains, so I blended a cloud material with my Air material. This method works better, anyway. I've included two cloud VOBs with two versions of the material on them for you to download. Click here to get your goodies!
Create a terrain and double click to edit it. Get rid of that silly crater that always seems to appear first (at least in mine) and put in a nice 'Mounds' terrain. Hit Dune a couple of times, 3-4, then go to the Effects tab and click on Stones. Click on Stones some more (just tap-click, don't click and hold or you'll create tree trunks!), and toss in a few Pebble clicks in between for variety. Clip the lower end of the terrain spectrum, then press the Lower Edges button. You should end up with something like this:
The cloud mass will look best if you shrink it perpendicular to the camera; make it a rectangle. You will also probably need to shrink it vertically; do a test render to get a good height. Your 'stones' should be broad curves, not tall towers. After squeezing things down, grab the proportional sizing handles and make the clouds humongous. Move them far away from the camera.
I tried making undersides of the clouds by mirroring a duplicate, but they never turned out right. Especially if I tried to Boolean Union them... then I crashed! So instead, I tilt the terrains towards the camera. (Hint: it is easier to size and rotate things if the camera is on the side, instead of at that silly default 45 degree angle!) Here is a side view of the above picture, showing the tilt and stacking of the cloud terrains:
here is the front view (note that I have the camera at the front of the vue space):
the tricky part. I have created a Puff Cloud shader by mixing a default cloud
material (with much less transparency!) with my Air material. (Air
is handy, you can save it out to your materials libraries, and mix it with
lots of things, like snow to cover very complex vegetations. See
Nevertheless, it seems each picture needs it's own tweaking of the shader to get the clouds to look right. Depending on the lighting and atmosphere, you may have to tweak the ambience (of the cloud part), amount of transparency, the blending strip, the percentage of clouds to air mixture.... There are other things that don't show, like the murkiness colours, which I have made blue-white and purple. Tweaking is the key.
The second Puff Cloud VOB is from this picture:
Yep, this is that really cool Ray of Light by Nicholas Phelps. I took out the fuzzy sphere clouds and put these babies in. :) (And a few more giant off-screen spheres to shadow them.) PuffCld3 is the foremost cloud terrain; not spectacular in it's own right, but it has a variant of the Puff Cloud material on it. In the top picture, the bottoms of the clouds break up into little wisps, but that didn't fly on this picture. And the lower edge of the front cloud was hard and plasticky looking. But now it fades back nicely! This was achieved by tilting the terrain even more, blending the air smoothly into the clouds, and using world space so the 'forward' edge was more transparent than the higher back edge.
Also on these clouds, I experimented with putting the
air on steep slopes, which makes the sides tend to be more transparent.
You can see that in the middle, where the background orange streak
cuts through the sides of the puffs. The next layer of clouds had to
have this effect turned down, because the brightly lit yellow tail end of
the furthest clouds showed up rather clearly through the dark blue.
You can also see a fault in this image in the lowest bank, the straight edge of the second terrain is showing up rather clearly cutting across the puffs. I'll have to keep tweaking....
Here is a view of the cloud banks in this image. You can see how they tilt towards the camera (very awkward when everything is at 45 degrees!), and how large they really are. The giant spheres on the left are the things casting shadows over everything. If they weren't there, everything'd be an eye-hurting bright yellow! (Try rendering the scene without 'em!)
Experiment and good luck! :)