Here's how i did it:
1) Always use the flakcanon
2) Just keep running laps around where the shield belt is and run above where the invisibility belt is. Don't stop, just keep running.
This way you always have a good chance of getting the armor/invisiblility first. And with the flakcanon you can run away from, face backwards, while shooting the flak down the hallways. So the flak pieces bounce off the tube-like walls and hit him. I killed him 75% of the time without seeing him. The flakcanon ammo is below, so every so often you will have to grab that, but then keep doing laps.
3) Then drink a bunch of brewskies (if you're over 21 of course)
Happy Fraggin'
:|