There are five Rampages you must complete as Trevor to unlock this achievement. These don’t become available until after you’ve completed the Strangers and Freaks mission that introduces you to Rampages. This mission appears after completing the first of the Chinese missions. It is located on the south side of the Alamo Sea.
The second Rampage didn’t become available until after arriving in Los Santos with Trevor. The rest appeared as I completed them. These missions show up as an orange skull on the map. You must get a certain amount of kills and survive until the timer runs out. You’re given weapons to use with infinite ammo.