Just build an MDT set and Atma for particular fights. There are plenty of times where the mob will do a GAIV and I'll swap to MDT to be hit for 0-100 damage while others are taking 300 and up.

Twilight Torque & Augmented MDT Dark rings alone can get you a good boost toward where you need to be.

Stack elemental resistances in slots where you can't get MDT and HP in the other slots. With Thieves tanking now more than ever, you'd do well to have a decent set of gear to shave off that damage.

And don't neglect those elemental resistance atmas. If I'm doing a big NM with a particular element, I'll use resistance Atma/RR/Apoc. The amount of damage reduced far outweighs the bonus of VV for whatever fight in question.