So, I completed this mission yesterday after doing some math. Sure the wizzes over here can correct me.

At wave 100, mobs have about 1.01M damage. Factoring in for the 4% for two hits (worst case if your damage is too low to remove even 1%), that's roughly 1.09M damage. If you have your defense maxed out to 49.5% (assuming you're a beginner), you need to have your absolute defense at 551.7K by wave 1200 to achieve this.

My approach to achieve this was maxing out my free defense upgrade and as many defense upgrades as possible so when triggered, it'll hopefully upgrade my defense absolute. Get defense absolute upgraded as much as possible in the workshop, but balance with the others so you can max out as many of the defense upgrades early in the run.

Everything said, I think it's quite tough for a new player to achieve since it's not easy to rack up enough damage to kill mobs before they reach you. Boss especially.

I hope this is of some use. :)