Once you're stocked and primed, jump into Trevor's truck and drive over to the biker gang waypoint. From there, a short cutscene occurs followed by a chase!
GOLD MEDAL REQUIREMENT: "LOST AND DAMNED
Use drive-by shooting to get them both.
Get in the truck and follow the gang to their hideout. Midway thru the chase, you can go off-road and find a Stunt Jump just to the left of this bridge. It's not necessary to do the jump but you'll achieve your first USJ if you do.
Once the gang arrives at the trailer park, take cover from the left side, while shooting whoever is closest. Trevor will only have a Shotgun equipped so you'll need to move from cover to cover to do some bad damage.
There is a Health Pack just up the road near pickup truck, so grab it if needed and continue up the road and shooting and taking cover.
"MISSION NOTE: RAGE ABILITY
Your radar will occasionally reveal bikers zooming toward you in vehicles. Lay in wait and pick them off from cover as they pass by. After several of the bikers are gunned down, the rest will retreat and run away from the area, leaving Trevor and his crew alone. From there, get in the truck and drive to the next waypoint.
GOLD MEDAL REQUIREMENTS: "TRAILER TRASHED
From there, either shoot Ortega or walk away.
Once that's done, get back in your truck and drive home to complete the mission.