I did it same as you and just with one blue tower between two machine guns down on the bottom entrance and on the first time I made 188 diamonds 🤩 perfect 👌
Its way so easy with another formation with adding some support towers on last wave + there is a trick about using double speed against the boss while putting boxes The odd is since 2x speed means increase attack speed, but here on the boss its damage to boxes/barricade almost same with or without using 2x speed, so keep put boxes while activate 2x speed when the boss in middle area, it would only cost 7-10 boxes or 21-30 golds Yet when i tried "without" use 2x speed with same formations it mostly cost 13-20 boxes or 39-60 golds No idea how its happening like that lol
