2fort's (and Byre's, if you're curious) clouds are just a giant cylinder around the map in the 3dsky that slowly rotates. Super cheap, and dynamic.
Yeah, but those clouds are 8 years old now and really low res, and they also just cover the horizontal plane. Besides, they don't work so well for 90% of the skyboxes since most of them have some sort of mountains in them, and puffy 2Fort clouds just don't form there.
If we can upgrade the cilinder to half a sphere, then we're talking. Or we'll just have to make a giant cloud dome model with cloud textures that has a looping animation and an alpha channel to make it transparant in the places where there aren't any clouds.