1 - Build the blockads and explosive traps in these spots for 1st wave
2 - Build these striker towers next - make sure they cover the side blockade, and front blockade
After those are done build whatever. You should be able to have everything built after the 3rd wave. Then start upgrading towers, but make sure not to overspend in case you need to upgrade a trap or barracade in the middle of a wave to repair it.
If you're having trouble with the barricades make sure you don't upgrade them all the way so you have room to upgrade in the middle of a wave to repair it.