Equip a tanky Warframe and build your weapon for radiation. Choose one of the 3 Isolation Vault bounty. The higher the bounty stage, the more Necramechs you need to defeat.

Stage 1

Go to the Bait station and collect Fass Residue or Vome Residue throughout the Cambion drift. Once you've collected them, return to the bait station, insert the residues and defend the station. Once you've successfully defended the station, take out the bait from the station, go to the marked location and throw the bait at the infested door.

Stage 2

Kill marked enemies to survive.

Stage 3

Try to take on one mech at a time. Every mech has two weak spots: Engine on the back and their shoulders. Otherwise, it is invulnerable.

Shoot its arm oof first. The mech will only charge at you and can't use its weapons. Avoid being charged by it. When it hits a wall or an object, it will get stunned and you can attack its back.