6-long DU Buff Beam from the top of the wooden post to the ground at the corner there (hint2). Gas trap controls that NE pathway really well.
Party: 1 TB monk, 3 summoners with monk/huntress pets
Note: If you don't care about the monkey pet, the best time-for-your-money run is gonna be 25-35. The mob numbers are up slightly and the speed of the waves drops considerably (like 30 sec per wave).