i have just beat lvl 8, was more luck then anything else cause if the zombies wanted too they could have killed me...
i guess that makes me not eligible to leave tips but
1: floodlights kill the guys at the same time, preventing one wave from eating each other.
2. lots of trucks.
3. concentrate building space (base should be max 4 by 4), plus floods will get you through day 3.
its all good till it gets to the ships- WAY too long range dude. fix the ship lvl please because the only way to beat it is if you played it before and know where they coming from which is not good design.