Two mana chests gives enough to build everything and up the beam 3 times. Have just a TB out and upgrade the rest of the beam while boosting during the wave. Aim your chickens at the east crystal for the most part.
I also tried this with 3.7k Tower Boost instead of 7.7k Tower Boost. The combat time was just 2 and 3 seconds longer for the waves.
Remember to put your splits in during the middle of Wave 19 to get more Owls.