TEM and I went through this exact problem a couple days ago. I wish I could give you a good strat but there isn't one. It's literally nearly impossible. Just try to have as many shots as possible heading at the tower as you cross the threshold which makes the tower vulnerable and the turrets start to shred you. Then keep shooting as fast as you can. Active reloads are a must. It's also helpful to immediately slam against the back wall once you activate the turrets, but nowhere is really safe. Note that moving offsets your shots from the aiming reticle, too.
It took us probably 50 deaths and massive luck.
