Iron Brigade

This is the final mission of the DLC, called "The Cathedral." If you have upgraded weapons this is very easy. Simply direct ALL fire towards the building and ignore all the enemies. There are three stages this will go through. Equip the fortify/quickload legs and your strongest weapons and just sit right in front and fire. I did it in 86 seconds with just one other person.

This is also a great stage to boost XP on if you have at least one other person. Have one person equip dampening generators, and the other equip a repair crane. Put a repair crane on each side when you have enough scrap, and build a bunch of dampening generators near the spawn points. Have each person sit next to their repair crane and kill all the enemies (and ignore the boss). In stage 2 you'll get infinite Breakers, each worth 60XP. It's nice to have a third person so you never have to leave a spawn open when you want to switch sides. You'll get a bunch of loot this way too. I'd caution to only spend 30 min. at a time. We were playing for 40 min. and the game locked up, so we lost everything!