You need enough aura range to snag the 2 auras with 1 4 point buff beam. Remember to pre buff both aura stacks with temp buff beams before placing final 4 point and deleting the temps.
Don't upgrade the proximity mine trap. It can get despawned. Just heal between waves as necessary.
I use 2 Boost guardians 1 Apprentice 1 huntress.
I also use a tower boost monk on final wave. I stand ontop of the LT towers.