Thanks @Chilese. I'll look into it. And @MichaelChandra: you can avoid the energy problem if you stockpile 200 energy before you build the mortars to clear out the sea on the right. At least, for long enough to clear it and build across to get more energy.
Worked for me, at least :)
@MichaelChandra: it's possible, but takes a lot of time: just spam reactors in the beginning then build mortars, and move the mortars across the map if you have to stop the Creeper from building up too high.
Eventually I had about 10 mortars and began to gain on the Creeper, slowly driving him back.
@OldFern: you actively have to turn it on, by pressing the small button on the bottom below the "play more" button. The default setting is not survival mode, but standard mode. If you need more time, just use the [||] (pause) button that is to the left of the options button.
 "Creeper World: Evermore"){kind=icon}
 "Cursed Treasure: Level Pack!"){kind=icon}