I've only just realised i can build plasteel auto turrets and its an massive game changer when defending mechanoids and raiders (haven't tested with tribal armies due to good relations). I find that the turrets take so much longer to be destroyed and with all the dead mechaniods there is more then enough plasteel to rebuild and store some for a rainy day.
I recommend you try them if you already haven't.
I recommend you try them if you already haven't.