Fog Mercenaries
Directly inspired by this mod:
Gas Mercs
https://steamcommunity.com/sharedfiles/filedetails/?id=2804741547
Adds a Mercenary Guild squad with protections against Dust, Gas, Acid and Burning. They are homeless spawns that only appear in the Grey Desert.
I picked the Grey Desert because it is connected to three of the most environmentally dangerous areas (The Deadlands, The Black Desert and Venge).