I did it in my forward hatch. no problems with the hole saw. I changed the angle of attack by slightly wobbling the drill to give the blade room enough not to bind as your going through. There are directions with the vent.
BTW I've had issues with my vent, the second one failed. I will try replacing the motor that someone suggested on this site or the Cat30 Yahoo group. Good luck, mine has never leaked and when it works make a big difference in the cabin odors and temp.