Thanks a lot, nice job
About CG-Texture, last time I go there, their skybox was only skies ! I mean: there was no ground (like mountain, canyon, hills, or plain).
This is great for "skybox entity", but not really usefull for classical cubic skybox.
* If you want to give us a ready-to-use skybox, jpeg 512x512 is fine, just do it with at least 80% of jpeg quality, under 80% there are visible jpeg artifact.
* If you want to provide source at the original output size of terragen, just convert them to PNG-24 (BMP file are a little too big, and PNG is non-destructive too). Or if you don't have anything to export PNG, just export a jpeg at 100% quality.EDIT:
I didn't find your sun in this skybox
And about sun, if possible, can you put in your README.txt the coordinate of the sun you have set in Terragen ? It is really usefull for mapper to have the sun coordinate, because it is what we put in the skybox shader, this allow us to cast shadow at the right angle