Supertank has an indestructible turret at the rear, too >_>
Well, I beat it, anyway. Lancers kept dieing before they could even get a shot (which misses 99% of the time >_>), so I just filled the trenches with shocks and snipers and got some scouts to climb the ladders after Welkies dealt with the turrets.
Selvaria thought it'd be smart to guard the last ladder, so I ended up having to make a barrier (with my tank) to block her shots while Alicia 'naded the radiator :P