Ok, I've made it to the unlocked missions (finally). The 'Waste Disposal' map is impossible IMHO. I've tried it a dozen different times, improving on my strategy and minimizing spent resources. I've routed the enemy the longest path possible while using the fewest towers possible, and passing by many towers twice.
No matter what, once I get past level 12 I get hammered. It seems the stealth units are nearly invincible, even though they're being pummeled as much as the other units . And I have a couple command towers near my clusters of attack towers so that they are detected.
It would be really nice to be able to take a full map screenshot so I could post it to show others that may be able to help me.