I think having two turrets on a newly upgraded Bunker would serve as a formidable addition to this defense. Having a level 4 bunker that would target two enemies simultaneously would be a great upgrade!
It is awesome when visualized, but we need to consider balance. No matter how good a structure looks, it's no fun if it's broken.
I would love if the next bunker upgrade had 5 gun turrets instead of 3, and if they where shaped like a pentagon with a turret in every corner. Everything else (maybe not, but a lot at least) in this game is shaped like that, like the cannon and mortar muzzle.
I think bunkers are already powerful enough with a single cannon. My gosh I can't imagine winning against a base with 4 bunkers x 5 cannons each. The game is not called "Mission Impossible ".
Let's just throw in about 5 extra flame gates. And at level 4 they cause continual burning after walking through.
I want my GP's to be able to be set to shoot in a direction of my choosing attackers would have no way to know which way it would shoot from when planning an attack
Maybe not now, but in the future when the pirates we use have got even stronger we will need another more powerful bunker!