Camp the room that has the trader on the middle level thats like the 2 similar rooms right next to each other. Just use the bullpup or AK for the early waves, but once wave 6 hits, you should have a crossbow and a scar since it's the only AR you can carry with the crossbow.
Use the crossbow on scrakes, 2 headshots should do the trick. Just make sure you wait until he becomes unstunned for the second because it's a more reliable shot in the sense that the hitboxes will be where they look like they should be and it gives you some time to pick trash off from around him.
If a fleshpound comes lumbering in, your best bet is to run.
As long as you're ALONE (important) you shouldn't have too much trouble not dieing as long as you're a good shot. Just make sure to watch both ahead and to your left.