I have been doing the above strategy. I am using a DPS monk for my main play character, and placing walls with a Squire, towers with my Apprentice, auras with another monk, and traps with a trap huntress. I pre-place an Inferno, Proxy, and Electric aura on my "battle zone" for the boss, and after the last round is over I sell my wyrven defense and put up Snare + Heal and I was able to get her to 1.2 million as I said but I just can't do the damage.
I think my issue is I can't really capitalize on the chest opening. 9/10 times I just get webbed by something or other and I get one, maybe tw