open this:
_zombiemode.gsc

find this:
maps\_zombiemode_auto_turret::init();

put this:
maps\scavenger::init();

underneath this:
maps\_zombiemode_auto_turret::init();

so it looks like this:
maps\_zombiemode_auto_turret::init();
maps\scavenger::init();

put this:
scavenger.gsc

in here:
mods/mapname/maps

