I find that shot guns and auto weapons help immensely in the cave, as for the darkness once you get 600$ usually around wave 2 or 3 for me you can activate the generator lighting up the rest of the area beyond that the little light that's outlined in red next to the tent can be picked up with E and taken to wherever you want to try and hold off the insects you can drop it and all other guns with the G key and the light will point in whatever direction your facing. beyond that its just skill and knowing the enemies animations, good luck. :)