If that fails... putting some greens and LED taplights in there before they start to find a roost for the night may encourage them to figure it out. If I know there may be a storm rolling in I usually just put a LED lamp out in the coop. If there's a light in there everyone will come indoors...
They will huddle and sleep in piles, even if warm... just a normal baby/chick thing for safety :)
I agree though- they will figure it out.
If you want to speed them up, just physically put them in there at dusk for a few nights. If they feel safer in there they will be more inclined to...