It doesn't help that 9/10 it's just a duo.
Just to be clear you do understand the mechanics of that fight right? You shoot the legs until they 'break'. Every time a leg breaks the tank will outstretch it's neck and you shoot the glowing red neck for major damage.
You can see a red laser where it is going to shoot it's OSK attack. If you see the red laser coming at you, just move.
Use one of the sides to stay in cover and adds won't come at you - or the back to cheese it with no adds at all.
It's a pretty simple focus fire on a leg until it breaks, then shoot the neck, hide behind cover when it aims its laser at you type of fight. Doing that you shouldn't have too much of a problem at level 7 or higher.
Oh and also, you can't run out of ammo in this game. If you use up all of your ammo just wait a few seconds and the game will restock it for you.