attacking watch towers with 110c gives 0 losses
Here's a pro tip: If you add 1 troop of every kind to any of the tower attacks, you will see the destruction bar count down faster, thus less wait.
For myself, I use 1R 1M 1S 1E 125C 1B 1LB 1K (I realize not everyone has K, cannon, but even so this shortens the time you have to wait for the bar to disappear).