This location is much more shielded. I was able to get the achievement first try using this location on the "Sandy Survival" job. You can bookmark the job here so that you can open it in-game:https://socialclub.rockstargames.com/games/gtav/xboxone/jobs...
Other general tips:
- Buy as much body armor as you can from Ammunation before starting survival.
- Buy lots of snacks from convenience stores before starting survival. You'll use these to replenish your health during combat.
- Wear your heavy heist armor and bullet-proof helmet if you have them.
- Use the interaction menu to refill your health and armor during combat if necessary.
- Pick up ammo, health, and armor between rounds. It should all be right out in front of you if you use the location above.
- Get back to cover before the between round timer runs out.
- Use the minigun on choppers if you have access to it. If not, homing rockets don't seem to track so use a high-powered rifle to take out the gunner and pilot. Try to use the surrounding roofs as cover when you're reloading or taking fire.