Use a group consisting of 10 Gunners, a few Iron Storms, a couple of Choppers, and 10 Bombs. Having high level Pyros from clanmates will help. Being your attack near the gold statue inside the base, with 5 Gunners to each side, then 2 Iron Storms. Quickly launch a few bombs to breach the nearby walls. Launch the other 2 Iron Storms and the rest of the Bombs. Then, use the high level Pyro and the Choppers.