(clouds that is.)
Okay so im having some issues with cloud design and i hope you all can help me out.

Here's the scene im working on.
In the foreground will be a couple jet's dogfighting.. but i thought to add a nice extra layer to the set, and to the animation, it would be cool to have low hovering clouds over top of the landscape.. and that they would cast nice shadows on the earth.
Now i've tried using particles to create individual cloud puffs and it does look good.. but it's going to be pretty taxing on the processor to produce soo many particle clouds to get realistic effects.
so im wondering if there's a shader out there i can apply to, say a large box, that will fill it with clouds (volumetrically i suppose) for an equally realistic effect.
thanks a bunch..