CloudBuilder is a free series of Photoshop actions that accompany the 90+ HDR Clouds with masks.

These can be used in game engines as static or multi layered skyboxes, 3d rendering programs or as a backdrop for matte or concept painting.

90+ HDR Clouds with masks - http://cbr.sh/tuqtxm

Example workflow can be seen here - https://youtu.be/l8ETpPUEhOc