This is an old problem. You add a fort in the battle editor, and try try to play the battle or reload it in the editor, and the fort is gone. RTW doesn't save the record of fort in the battle editor.
From googleing it, people have figured out the record of the forts need to be add manually in descr_battle.txt .
But how exactly I do that? I trying changing "level village" to "level fort" but it still give me a village.
I need help, desperately.