Story related, cannot be missed.
You will be given a task by the Sheriff of Wellspring to delivery more supplies, but he states you will need a better vehicle first. Your tasked with heading over to Jackie Weeks and talking to him. He will tell you that you need to get sponsorship from the guy who runs Mutant Bash TV named JK Stiles.
Follow your waypoint to his studio and he will of course want you to go through an "episode of the show". It's essentially horde mode for 5 rounds. On the higher difficulties it gets challenging so remember to constantly be moving and strafing. I relied heavily on Wingsticks when I was reloading. Bring a lot of ammo and health but you will get minor resupplies in between some of the waves. Survive the final boss on round 5 and the achievement is yours.