The tutorials on how to place turrets on units reminds me of when I took a Computer Graphics course... Going through a 200+ step tutorial printed in small text in a 1,500+ page book was a freaking NIGHTMARE. Then if you mess up at one part, you have to re-iterate though ALL of the previous steps. It's like being boxed into a prison and all the data and parameters are the walls.
So ya... I think Blizzard should make an intermediary for unit creation. It would kind of be like the cutscene viewer/editor to my knowledge. It would be nice if such an 'unit forge' could be accessed by just simply right-clicking on a placed unit or though the data editor.
Once you go into the unit forge, the respective unit could be modified using various tools that include placing objects. So instead of spending a several hours like I have trying to place a turret on a moveable object, you could just simply go into the unit forge and place a turret on an unit. Plus all the custom attributes and additions could be localized to a specific unit, so creating / managing a map with numerous modified units wouldn't be EXTREMELY difficult and time consuming.