Shantytown - Respawning Enemies at Helicopter Hill Base Camp

If you want to collect more salvage, after using the base camp, reload the autosave from the pause menu. When you do, several enemies will appear off to the left and move in on your position. It's nowhere near the huge horde that attacked the first time though. You can shoot some of them from the starting position.

If things get tough, the corrugated metal barrier to the left gives decent cover from the men shooting from the building.

You can then shoot at the individual men as they come up the stairs on the right...

...or take potshots at you from below.

Just watch out for petrol bombs and dodge out of the way as needed. When you've killed these 3-5 or so guys, loot their bodies. Then use the camp again to trigger another autosave. Reload and repeat. Small groups of enemies will continue to respawn so you can collect salvage until you're ready to move on.