Brooke,
If you have saved any terrain tables for the particular terrain you chose for the mission, the name of those tables will show up in the pull down menu. Select one and when you upload the file to the server and someone checks the box use mission arena settings in a custom arena, it will load that table. The table is uploaded when you upload the staged mission. If you saved a table under the name Tunisia, that is why it shows up. The saved tables are listed in the individual terrain folders in the chconfig folder in AH. Offline, I think you have to load the table, but I am not sure about that.