one thing I have found...if you edit the description.ext, you have to completely reload the mission for it to take. So if you alt-tab out of the editor with your mission even in the editor screen, change the .ext and then try to preview the mission, the change won't be there. I always save my mission, load another in the editor, alt-tab and change my .ext, then alt-tab back in, reload the mission I am trying to change, and the .ext will be updated.
The .ext seems to be the only file that requires this.
Related issue.....
to make life easier for a number of reasons, I have creted a map on each island and named them desert blank, everon blank etc... I just created a new mission, put in 1 unit as player and saved as named above, this has been an enormous help in several ways for me