For this you need a minimum of 6500 points
to buy all the necessary doors to activate the artefact and open the Cargo Hold area. You need to survive 5 rounds in a row without leaving the Cargo Hold area. Ideally you will want to this on a low round a possible. Once you get to the Cargo Hold area, I would advise draining the water in the Cargo Hold and buying the Titan off the wall when you can.
You will mainly want to camp by the Pack-a-Punch and keep on using your specialist ability and your equipment. I think the Hammer of Valhalla is a great choice for this.
Good Elixirs to have are as follows...
Overall I hope this helped you out.Call of Duty: Black Ops 4 Stowaway Achievement Guide