Use the first 4 rounds to knife zombies and save as much money as possible. Avoid nukes. I like to shoot them before I knife them for extra points with the welling. You should get to the poop deck and grab the Sentinel Artifact which you will need to open the cargo hold. Once you grab the artifact head back to the front of the boat. At this point you should be saving money to grab a weapon you want and open the last door to the cargo hold. The VAPR in the mail room and the Titan on the back cargo hold wall should work fine.
This can be done in casual.