I was listening to the audio book version of Stephen King's "The Mist" (I tried to watch my copy of the film, but it wont work in the player anymore

) and it started me thinking of using the idea for a SA game.
Setup - place a number of buildings and some obstacles like fences around the board. Place the Agents on the board - anywhere the player likes.
Starting with turn one mist will appear. I was thinking of cotton wool thinned out on a base to represent mist.
Roll to see which side the mist arrives on, and it will travel to the opposite side through out the game.
Each turn more mist (1d6 mist bases?) adding to the thickness of the mist.
Lurkers - the mist brings nasties with it. Any agent in base contact with the mist may be attacked by a tentacle, giant stinging flies or spider things.
Each lurker is of low level power, but there will be many of them - roll to see what appears in the mist each turn too.
I was thinking that the game lasts until daylight arrives - so there will be many turns. Maybe make one turn the equivalent of 30 mins giving 20 turns, or one hour giving 10 turns. Maybe more turns with a smaller time scale.
Agents can try to flee, but only if a) they go insane, or b) there is mist all over the playing area... i.e. they can't leave before the mist arrives.
Any suggestions for better mechanics, figures to use for the lurkers or other thoughts most welcome.