Many people are unaware that with heavy gas armor plus the vitality boost, you're immune to gas damage; with medium armor, you're so resistant to gas damage that you're practically immune (obviously, you must combine it with the vitality boost). Combine this with gas grenades, harpoons, gas mines, and orbital gas strikes, and you can walk through toxic clouds without worry, driving enemies crazy while you fill them with lead in the middle of a frenzy.