Savage Air Flow
If you're using a pickup body you probably don't need to (some variance depending on ambient temp and how many fins stick up above the body in the back.
If you're using an SUV body or something else that cover the head, then yes, you should cut 2, one in the front and one in the back (think air flow, not air flurry). I use a holesaw in my drill to cut the circles, fyi.
pb