Hello, I've been very frustrated on this level for few day using many strategies that I can come up with but no luck. Always gets killed by 18 or 34th wave.
But today I did something without even thinking if it actually works... Placing all rocket launchers right at the entrance. As many as 21 fully upgraded rocket launchers and guess what. Yep, no critters came through, didn't even give them a chance to heal. I've put 6 flame thrower up the hill close to the entrance. At maybe about 80 or 85th wave. Some critter went through but still get blasted away by the launchers up on the hill. Just when it's almost time up, I put three scrouts about 3 block away the entrance, upgraded them just so that they can hit some critters when they actually slip through my arsenals of nukes.
I haven't tried this method on hard, but with careful placement of flame throwers, nukes, and scrout, its probably fun to see it happens.
Awesome game btw