I GIVE ALL CREDIT TO RABIDKITTY4.
Not trying to take credit or anything just improvement.
Use Rabidkitty4's guide go ahead and download his gametype
EDIT: if you want I have uploaded the game type on my name, it is called "Hard Chevo" so just download if you want.http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=35867...
make this one change well technically three.
1.Change all Enemies to Elite Generals
2.Play on Corvette
3.Turn off Dropship spawns make sure they are disabled.
Change all waves to Elite Generals everything on every wave even on the bonus change to Elite Generals. Make sure bonus wave time is at 2 minute. Now just fly around and use your rocketlauncher and in less than 30 minutes (got mine in about 19, you can check my service record) you will have this cheevo, I may have gotten lucky (doubutful though) but on my first bonus round i got about 550,000points maybe a little more.
And you know the more people the faster so...good luck.