You don't need of tools dude, let me teach you:
-Open the World Editor
-Open the Import Manager (F12)
-Import the Ballista (Model [Blood Elf Obeliskv2.mdx] and Skin [BE_Ballista01Test.blp])
-When you import them, will apper "war3mapImported/Blood Elf Obeliskv2.mdx" and "war3mapImported/BE_Ballista01Test.blp", just remove the "war3mapImported/"
-Save the map
-Close the World Editor
-Open it again
-Open you map
--DONE--