I've been there to witness some fairly strong gusts of wind and the hoop part barely trembled.
They are using, or were, both the nest boxes in the new coop and the one in the old coop. From this I think three nest boxes may be best for them so a nest box addition, even if it's the small coop should be adequate.
C tells me most shelter in the new coop during the rain, some even going back into the coop for a while.
I have enough materials left to make another smaller tarpaulin shelter which I am think of doing. Something half the height of the new coop might work.
I've asked C to get some pallets from her local contacts so I can make duckboards.