If you got a brand new radiator, I wouldnt bother. It is new, so should be sealed. Unless you got a new one without the tank, which I have never seen that. Mine was new 3 years ago and no issues to this date.
Just get the O-rings for the tank for a $few. RTV will make this a nightmare to remove in the future.
Why won't you be using the bleeder screw? How you going to bleed it?