You obviously don't seem to get my point.
Which program do you use to make skyboxes?
There are many. SkyPanorama, SpaceScape, Terragen, etc.
I do, but anyone who does that is handicapped. And because I love repeating myself I said that once done you'll have to package everything appropriately and that as far as "seeing a concrete or stone texture sky box" you are wrong. You will see the sky color that can be set with the sky environment.
Lol if it's such a big deal for you to copy and paste some files into a .zip and change the target within the .mis then do whatever aloof method you want.