I started by grabbing the white gem. This is difficult, but I hope one understands how I did it by the screenshot:

Then I rushed towards this configuration:

With the two CBs you saw me constructing, I took a bit of the chamber below my position:

It was then a matter of digging further for reactor places, whilst massing CBs to defend my position:

Using 2 simultaneous CBs I was able to nullify the emitter in the chamber, then proceeded with my defence and build-up.
I decided to replace my shields with repulsors after a while (note also I had to double up some repulsors to keep the creeper out (I learned this the tough way... by dying again and again):

This gave me a lot of time to construct 5-6 CBs in reserve:

With those, I took all of the subterranean chamber, and this yielded enough build spots to get to the required energy production:
