Hard Truck: Apocalypse - Rise Of Clans Help!

[Sergeant-Coates1]

For those who have played and beaten the game, you will know what i am talking about.

I am stuck on the part where i have to be in a turret and destroy all the robots coming at me, with an irritatingly slow reloading shotgun. No matter what strategy i use, i can not keep robots from infiltrating the base. What do i do?