At this point, no. Outdoor maps still have broken front-middle-back differentiation code. The only way I could imagine preventing the objective's destruction would be to put stuff in the mission that will completely overwhelm the base defenses. Unfortunately, that will make it very difficult for the players of your mission, so it's not a very viable option. 
"If I had Force powers, vacuum or not my cape/clothes/hair would always be blowing in the Dramatic Wind." - Tenzhi
Characters
Instead of making them "destructible" make the "collectable". Then the firebase won't shoot at them.
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or defendable - that makes the enemy rush reinforcements (and the firebase will destroy those)
The map doesn't support collectable items. I'll give some thought to the defendable option and see if I can stretch the story around it. I wrote the story arc around the final map and premise of destroying said object not realizing until after I'd spent two weeks on story, NPC chat, clues, etc that the map didn't differentiate placement areas.
I really wish they would fix outdoor maps. At least this map. Gun turrets and soldiers that can defeat mission requirements is a problem.
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Does anyone know a way to place items on this map and prevent the firebase from defeating them? I've tried everything I can think of, even loading the map with the maximum number possible of optional objectives (patrols, battles) and still have the required objectives still frequently spawn on top of and be defeated by the firebase.
Together we entered a city of strangers, we made it a city of friends, and we leave it a City of Heroes. - Sweet_Sarah
BOYCOTT NCSoft (on Facebook)
https://www.facebook.com/groups/517513781597443/
Governments have fallen to the power of social media. Gaming companies can too.