I will watch this, but in advance I will say that Mumakil are intended to be really strong against Goblins (and Isengard) so you will have a hard time. Your only option that I can think of would be a crapton of Goblin Archers with Fire Arrows (super fast tech), or maybe Spider Riders with some awesome micro. Not sure if Drogoth would help or not. All of your other units will just die.
Actually I'm curious if maybe Trolls would work, or if they would just get trampled, too.
Spider Riders would have helped way more against the enemy. Cave Trolls were OK and good at harassing, but Spider Riders can harass too, and obviously would fare better against masses of Orc Archers.
