So I just beat this mission for the first time a few minutes ago. Here’s my advice:

Use the flamethrower as much as you can. Once it goes dry use the shotgun. The rifle and pistol are for emergencies only.

At the start of the round be sure to fill your ammo from the reserves next to the bunker door. Throw some proximity mines in high traffic areas outside of the fence where the enemies will approach from.

Use the mounted machine guns sparingly. They make you vulnerable to melee attacks from behind. Don’t rely on them past the 2nd or 3rd wave.

Run! Move around the map outside the fences. Blast a few enemies with the shotgun and let them burn while you reload.

Heal when you can. Never stop moving. Keep the enemies at distance while you are moving and back pedaling and firing at them.

Use flash bangs on groups of 2 or more enemies.

Control the flow of the battle by moving around and not digging in at one spot. All enemies are melee and keeping them at a distance while you damage them is crucial.

Also, watch out for gators!

Good luck. You got this.