This is a strategy rather than a cheat, but it is so easy it may as well be a cheat.

Best scenario - Have Wunderwaffe, Magnum (any anti-dog gun), Juggernog.

At this point, open the 1000 point COMM door to the swamp but not the 750 point COMM room itself (hopefully Juggernog isn't there, this will still work if it is, but not as easily with the COMM hut open).

At the beginning of a zombie round, walk out the COMM room door into the swamp, make a right and move along the fence in the grass until you hit the little shack, make a left and walk around the boardwalk until at the start point / keep repeating while avoiding zombies (just run past them and keep going - thanks Juggernog).

About the third time around, stop in the second shack (halfway around the circuit from the first shack) and fire the Waffler at the crowd (kills about 10 zombies), walk the circuit about 20 more feet, turn and fire (10 more zombies).

You should now have 2-4 zombies in pursuit, Waffle them or use your other gun to finish them. So 2-3 Waffle shots per round total. Kill dogs where you see fit with your Magnum (or gun of preference).

This will give you a Max Ammo. At higher rounds, just use the Waffler as the other guns hardly hurt the zombies.

I was told this strategy a while ago and I believe it is called the 'Vandt'(or similar) strategy.