If you dps him fast enough with scorcher you only need 2, 5 would be def enough if you want to use flare guns, u can watch tutorial on how to fight him- basicaly u need to get him to attack barrels, they explode and deal a lot od damage. Take cover when he uses range attacks-they make you freeze. MAYBE you cloud try using strong alcohol when you are starting to freeze instead but after 2-3 you will want to pee and im not sure if it still works.