I only had to mine about a third of the map to win. I only mined rubies to finish the quest, sine I already had all the upgrades. Never mined a single diamond. I guess that is what happens when you let people leap frog upgrades. I still enjoyed it though.
Upgraded fire gas is really good, just place them right after health. DOT will take care of shields so you don't need to waste time on EMPs. Also, the AP turrets are well worth it.
If you are having trouble with the boss lure it back to where you spawned: there is always a vehicle there and you can use it as a barrier. Then, just edge over until you can either shoot the edge of the boss or explode a nade/rocket next to him. just don't get too close to the vehicle, cause the boss can shoot through it.