I have the same cooler. I just asked my LHBS that question last week. I believe the default value was 0.30. They recommended 0.35. I used that, but rinsed my cooler out with the garden hose (60-ish water) before I started. I ended up about 3-4 degrees cool. (146 and change instead of 150) I think if I had the cooler at 70 and dry, it would have been about right. I just kept some boiling and cold water on hand to make a quick dump in correction.
Primary: , Boddington's Clone, Mirror Pond w/Marris Otter
Bottled: Fullers ESB Clone
Kegged: Mirror Pond Clone
Drinking: BM's Kona Fire Rock, Dead Guy Clone, Alaskan Amber Alt Clone, Firestone DBA Clone, Magnum/Crystal IPA
Next up: Burton IPA