WowGreat price for a standing rib roast !
I'm just a newbi here, but an old veteran of preparing & eating "Prime Rib". They are my favorite, and I only ever had two that weren't great.
My guesses would be:
Bone side down, which would put most of the fat on top for natural basting.
I would not foil it----love that smoke flavor.
And if she likes it at "rare to med rare", I would get it out of there before it goes past 140* (that would be rare, but it should coast right into rare/med rare).
I have no idea how long this would take. I'm sure somebody will.
BTW: Those two Prime Ribs I had that weren't great were from two different restaurants around Lake Wallenpaupack, PA. They were 12 miles apart & their prime ribs has a lousy musky back taste to them. I asked a diner owner buddy of mine about it. He said both restaurants got their prime ribs pre-cooked & pre-seasoned, and out of the same delivery truck,ready for them to "nuke". That would explain it !
They should be ashamed !