Decoys (and a lot of luck) is your friend, friend.
I started by building 3 money centers at the west corner of the map, then waited for the plasma missile to cripple me... When it destroyed more than half the defenses I already have at the beginning, I simply restarted the game. In that particular game, I got lucky and nothing got hit at all, not even one of my bases. The money centers finished building, I covered my bases with camouflage (like always) and then built two diagonal lines of turrets to protect the money centers. All the while, I was firing the two upgraded and the single missile launchers I already had at the beginning to the western part of the ennemy island.
At that point, it was pretty touch and go for a while because of the ennemy golden (upgraded) Metal Marines. I got my northen defensive launchers hammered a few times but my money centers never really got threatened because the ennemy Marines never teamed up at the same time against the double turret defense. When I got thru the first wave of missile defense, destroying the hills with Metal Marines of my own, I also destroyed pretty much all of the Golden Marines of the ennemy and then had to cope with a
lot of dual missiles coming my way. It turned out that I got lucky and my main base didn't get hit much and I could easily rebuild what was destroyed in real time because of the steady cash flow, but all my three bases got discovered by lucky shots pretty much at the same time and I thought that I was royally screwed since even tough I managed to completely destroy the whole western part of the ennemy island, especially the money and energy centers, I was nowhere near enough damaging the ennemy plasma missile launcher or even the eastern side.
Trying to salvage the game anyways, I went into a defensive frenzy. My third and last HQ was completely behind my main base, so I built interceptor missile launchers protected by gun pods like crazy. When it was done, I built three radars in total and when the radars were built, I began upgrading the interceptor launchers too. However, even then the odd missile managed to go thru my whole missile defense once in a while and I knew that I was not going to win the war that way. That's when the idea of using decoy hit me. I tought "Oh yeah, you can see my last HQ huh? Well, look at that, I can build uncovered HQ decoys in my building list too! Here's something which will give you a few second thoughts for a little while!" and I built three well spaced decoys on each side of my main base.
The rest of the game was very easy. I always assumed that the AI of Zorgeuf the Great would be way better than the other computer opponents, since he is the last boss and all... Never would I have thought that it was so easy to fool him than to simply build a few decoys here and there. He kept sending missiles all over the island, and wasted a lot of time sending dual missiles on the fake decoys even tough he knew the location of my third and last HQ, decoys that I simply rebuilt in real time everytime they were destroyed. When he sent a few Marines, they also lost a lot of time running after the decoys, preventing him from attacking with missiles. He even spent his two last plasma missiles on far away decoys, sparring my main base again. :P It was only a matter of time before I got thru his defense and completely destroy the eastern side of his base, then the center up to the plasma launcher... Then destroy his HQ's and claim the win!